- This article is about general tactics regarding being effective. For the Hunter talent, see Efficiency (Hunter talent).
Efficiency is defined as "the ratio of the effective or useful output to the total input in any system" or, more colloquially, as "getting the most bang for your buck". In World of Warcraft, nearly every viable strategy is based on some kind of efficiency, generally minimizing or maximizing some value or concept. This makes efficiency complicated as a topic, however, because any given process can be optimized more than one way. What is efficient in one sense may not be efficient in another.
There are many ways to be efficient in World of Warcraft; however when most people mention "efficiency", usually they mean efficiency in one of the following (related) ways:
- Mana efficiency (that is, net effect achieved (usually damage or healing) for a given expenditure of mana)
- Minimizing downtime (that is, behavior that allows you to continue to act without stopping to rest or divert)
Other effects, such as maximizing the damage you do per second, while technically a form of efficiency, tend to be referred to as "maximizing" or "optimizing".
Minimizing Downtime When Grinding
Downtime is thought to be the enemy of grinding. The less you have to travel or stop to eat or drink, the more you can focus on getting XP. Minimizing downtime is usually equivalent to maximizing XP/second. Some general tips on this:
- Grind in places where the mobs tend to be near to each other (to minimize travel time) and respawn quickly (to minimize waiting).
- Healers should use bandages to heal.
- Casters should consider using wands, as these can reduce downtime by a larger margin than they reduce killing speed.
- If questing, try to deal with all of the quests in a specific area at once (to minimize travel time).
- Consider that downtime also includes skill- and profession-leveling or time needed to fill other goals. Look for ways to combine short-term goals (e.g. maximizing XP/second) with long-term goals. For example, if you are a tailor, you might consider grinding mobs that drop cloth to be overall more efficient than grinding those that don't, even if the cloth-droppers provided slightly fewer XP/second.
Minimizing Downtime In Instances
This is probably best covered by the Instance Grouping Guide and, possibly, the Talent pages for each class.
Mana Efficiency When Healing
A subset of mana efficiency is healing efficiency. With the large number of healing spells, gear buffs, and Talents that manipulate the math involved, it can be difficult to determine which heals are the most efficient. Further, there are multiple ways in which healing can be thought of as efficient. The two that tend to matter most are hit points healed per point of mana (HPM) and hit points healed per second (HPS).
Generally speaking, slower healing effects tend to cost less mana per point healed while faster spells such as 
[Flash Heal] and 
[Lesser Healing Wave] are less efficient, though this is not always the case ( [Flash of Light] being a notable exception). Spell power from gear serves to make things even more complicated, as some spells scale better than others with spell powers. For example, the druid spell 
[Rejuvenation] is relatively weak without any spell power, but scales to become one of the most mana efficient single-target healing spells in the game as spell power increases. As a general rule, however, spells which heal a lot per second (high HPS) will have fairly poor mana efficiency (low HPM) and vice versa.
Fortunately, there are web sites that allow you to play with all of these values. Having a rough idea of the relative HPM and HPS of your healing spells is vital to doing a good job as a healer, as frequent use of low-HPM spells in the wrong situations will drain your mana, while using low-HPS spells in emergencies will lead to deaths.
Mana Efficiency When Dealing Damage
Determining the method that delivers the most damage per point of mana spent depends highly on class. Gear and talents also matter a great deal. The formulas used in determining damage are varied, and can be manipulated in many ways. The Spell Damage Comparison page details much of this.
More info needed. Maybe class breakdown or links to such?
see: Hunter talents
Other Types of Efficiency
Many other types of efficiency exist in World of Warcraft. Most of these are better served by other pages, such as these:
- Formulas:Poison per second
- Talent Builds Guide
- Trap Efficiency
- Any of the class tactics pages.
- Hate generated per rage point while Tanking