Old style WoW horde leveling guides used to be written guides players could download and follow to power level using quests. These guides were very effective at helping those leveling horde or alliance toons by providing information and map spots that allowed a player to complete quests much faster.

There new WoW horde leveling guides are in game addons that provide directional arrows as well as way points and detailed quest information to guide players through questing in the different zone easily.

There are a couple things that are key to using these WoW addons for leveling.

1. If you are starting a new toon these addons help by starting off in your racial start are and guiding you through all of those quests.
2. Dying is the quickest way to slow down a power leveling toon because of the time you waste constantly running back from the spirit healer. These WoW addons ensure that you are doing quests that minimize your chance of dying and yes, this means even if you are leveling a holy priest.
3. There are tons of quests within the game on the horde and alliance side that waste time because they do not provide good reward for the time spent to complete.

The fastest WoW horde leveling in the game is via questing. this is the same for alliance and it is because of the experience awarded at the completion of each quest.

Even those who have played the game on the alliance side for years can find themselves lost in the game when they start WoW horde leveling because the quest paths in the start areas are completely new to them. It is almost like playing a completely new game.

When it comes to power leveling or simply being able to level a toon through quests without pulling your hair out, a good in game WoW addon for leveling can make the game much more fun to play.