Also, from a character building standpoint (which, isnt the most important) being a 10+ rogue gives you some bonus rogue feats, crippling strike, or imp evasion, although many of the other feats you can chose you get in shadowdancer levels anyway (so read up on which you get so you dont end up with redundant feats.)
Also, more rogue levels means higher sneak attack, so you'll do more damage in combat.