Resource pooling
Resource pooling is a tactic used to make the most of a class's resources at any one time. The idea is that when a limited-time bonus effect is active, the maximum amount of resources - like rage, energy, or focus - should be available in order to use many abilities in a row, causing them all to benefit from the bonus. This is generally used by players who have already mastered their specialization's basic rotation of abilities and reactions to fight events, and know when to alter their rotation to benefit even further.
Resource pooling could be considered a subset of the idea of "stacking" beneficial effects, except the "effect" being stacked here is "having many resources to use abilities rapidly".
Resource pooling is mostly a strategy for damage dealing, but the concept be applied to players in any role that anticipate incoming circumstances, like a tank pooling defensives for a heavy-hitting boss attack, or a healer pooling cooldowns for incoming party-wide damage.
Applicability
There are two kinds of abilities that need to be considered in this strategy - "effectiveness increasing" abilities, like the hunter's 
[Bestial Wrath], that open a window that a player can create a larger impact than usual — these are often also called "cooldowns".
The second are "capitalization" abilities that can benefit the most in a short window of time, like 
[Kill Command]. These are most often your "spenders", and are going to use your resource.
Personal or raid cooldowns, enemy debuffs, or even encounter-specific mechanics can all be considered "effectiveness increasing" the purpose of resource pooling, as long as they increase the impact of other abilities.
Many cooldowns are desirable to use as often as possible, and as such players should anticipate the expiration of the cooldown and begin preparing for the next pooling period. When such a cooldown becomes available again, the player can activate it immediately alongside their spenders ad infinitum.
In-practice
Due to factors like reaction time, lag, and the global cooldown, it is generally not realistic to wait until the absolute maximum resource cap, especially with a resource that regenerates quickly, since any delay after reaching maximum would cause potential resources to be wasted. Players may instead want to aim for a "soft cap" where there is still about 1-1.5 second's worth of "room" before hitting the maximum and potentially wasting resources.
It is easiest to pool energy if a player has control over the timing of the buff period, such as one granted by an ability or on-use item, but it is also possible in response to random or timed events.
- When pooling resources for an on-use ability, players can simply use the ability upon reaching the "soft cap" target.
- When waiting for a random effect, such as a trinket's random activation, a player may have to maintain a high level of resources for a number of seconds, by first reaching the target "soft cap", then sparingly using spenders until the desired effect is triggered and the resources can be depleted optimally. This ensures that even if resources are not at a cap when the effect goes off, they will at least be close to it.
- When attempting to pool resources for a timed effect in a fight, such as a damage vulnerability phase (see Witherbark's Brittle Bark in the Everbloom), or even the cooldown of one of their own abilities, players will want to estimate when the phase transition or cooldown will occur and start pooling resources early enough to reach maximum by the desired point. Addons as well as cues within the fight may help with this, but it is often necessary to allow for several seconds of error in either direction by starting pooling even earlier, and being prepared to maintain near-maximum resource levels for several seconds until the timer triggers.
- Coordination with or attention given to players that activate raid or buffing cooldowns is often helpful. For instance, if a player is aware of when a priest in their party will grant them
[Power Infusion], it may be beneficial to pool resources beforehand to try to get as many critical strikes as possible while the effect is active. If the only benefit of an effect is to increase attack speed and/or resource regeneration (e.g. a bloodlust effect), then there is no reason for pooling, since there is no synergistic benefit to be gained and resources may even be wasted.
Effects that increase the rate of resource regeneration, fight mechanics that slow resource consumption, even simple movement in an encounter all change the way resources are pooled, and require fight-by-fight strategy.
Example
A combat rogue's 
[Revealing Strike] increases the effectiveness of other abilities and lasts 24 seconds. If it is used as soon as possible, the rogue will have 0 energy after using it, and will regenerate 300 energy in the next 24 seconds (not including random energy effects), allowing the use of 300 energy worth of abilities enhanced by that single Revealing Strike. However, if a rogue stops using energy-consuming abilities briefly and waits until 100 energy to use [Revealing Strike], 60 more energy will be available for enhanced abilities during the duration of Revealing Strike, a significant increase. This saves energy and time that would otherwise be used reapplying Revealing Strike more frequently than necessary.
Mana and resources
Mana itself does not normally need to be pooled as the default state of mana pool is at a maximum. However, mana conservation in low-mana situations has similar strategies to normal resource pooling.
Charge-type resources, including death knight runes, are typically too inflexible to be "pooled". Since there are so few possible states for them to be in, it is difficult to pool a meaningful amount of them without hitting the "cap" where potential recharging is being wasted. Such charges are also usually quite restricted in their generation and usage, so it would be difficult to change their timing without reducing their overall effectiveness. This limitation is reduced with more charges and more flexibility in their use - for instance the rogue 
[Anticipation] talent effectively doubles the number of combo point charges, and stops them from being completely consumed by every relevant ability, thereby turning them from a relatively predictable cyclical resource into one that can be pooled for specific uses.
List of abilities
Please add any available information to this section.
These rogue abilities benefit from energy pooling:
[Shadow Blades]
[Kidney Shot], to pay for more 
[Backstab] uses (subtlety) and also for more abilities benefiting from 
[Sting Like a Bee] (talent)- Subtlety:
[Shadow Dance] and 
[Vanish], to pay for more stealth abilities and for more abilities to benefit from 
[Find Weakness]
- Combat:
- [Revealing Strike]
- The Deep Insight (maximum damage) phase of
[Bandit's Guile]
- Assassination:
- 35% target health, to pay for more
[Dispatch] uses 
[Vendetta]
- 35% target health, to pay for more
These warrior abilities benefit from rage pooling:
- 20% target health, to pay for more
[Execute] uses 
[Recklessness]
[Avatar]
[Colossus Smash] (arms, fury)
These feral druid abilities benefit from energy pooling:
[Tiger's Fury], but treating 35-40 energy as "maximum" to avoid wasting the energy from the ability itself
[Berserk], increasing the number of abilities that can be used at reduced cost- [Ferocious Bite], but only enough to ensure the maximum of 50 energy is consumed
The beast master hunter ability [Bestial Wrath] benefits from focus pooling.
The engineering tinker 
[Synapse Springs] benefits from resource pooling.
Players can gain an increased effect by pooling their resources before this ability from other players: