There are many reasons why power leveling is often desirable by hardcore players. But even for casual players, here are some compelling ones why it is very important to get up to level 60 as fast as possible:
(1) You can equip weapons at a higher level
A lot of the items have a level requirement. If you do not max out your characters level, these items will be deemed inaccessible. You will not have enough stats to be able to use the weapons or armor as well.
(2) You can't go on high level quests with your friends
One of the saddest parts of gaming is being excluded by your friends. If they are at a higher level than you, you will be excluded from their parties because you are not strong enough to attempt the quests.
(3) You can't access the skill tree
You don't get full access to all the skills there and because of that, you will not be able to experience the full range of your character.
(4) Making Money At The Auction House
When you are up there at the top, it is easier to acquire weapons and sell them.
One of the ways to level faster in the game is to find similar level friends and level together. Make sure you do not grind the same spot over and over again and be sure to diversify your items as well as the runes to see which are the most efficient skills.
Another way to speed up your leveling progress is to look up on various guides on the Internet and leverage on the expertise of others. This will allow you to see things at a level not accessible by casual players.
Lastly, be ready to diversify your strategies and don't stick to the same thing over and over again.