It depends on the character type.
![Razz :P](http://gamesas.com/images/smilies/icon_razz.gif)
But for the most part, it's about what the different types mean in terms of their character for RPing purposes, and also to find a new way to play the game. It's a new way to experience it I suppose. A self sufficient ranger may just live off the land and do minor jobs in town for NPCs and a bit of dungeon diving for extra cash, whereas a warrior type might go all out being noble and completing the MQ, and an assassin would possibly pick completely different quests to both of those other classes.
It also gives a different experience based on specialisation - so a character who deals in stealth and is a bit cowardly would deal with a situation much more differently than a wannabe Knight that charges in head first; just doing what she feels is "right" without really considering her actions beforehand.
It's all a desire I can't fulfil IRL
![Razz :P](http://gamesas.com/images/smilies/icon_razz.gif)
but I do it because I find it fun and interesting.