Power leveling in WoW can have many benefits. One of these many benefits and the most important one is making sure that your character get to max level as quick as possible! You want to get max level asap so you get to play that class and raid and pvp with the class with your family, friends and guild.
If you are trying to raid with that new class and character as soon as possible the way to go would be power leveling. Making a brand new character from level one and trying to get it to 100 can take days and sometimes even weeks if you don’t have the right amount of time played or short on time.