Balance makes it easier to have a fun game.

If you have a well-balanced game and want a well-balanced game, it's done.

If you have a well-balanced game and DON'T want a well-balanced game, it's easy to change it to match. Give advantages to those who are supposed to be more powerful-for instance, let's say you're running a game where you want three Joe-Schmoes and one elite warrior. Make the Joes level 1 and the warrior level 5. Bam, done.

If you have a poorly balanced game and want a well-balanced game, you have to put in a lot of extra work to make it balanced.

If you have a poorly balanced game and DON'T want a well-balanced game, you still will sometimes have to put in extra work. To take the same example from last time, if you have three level 1 Joe Schmoes and one level 5 elite warrior, but the Joes decide to play Druids and the warrior decides to play Monk...