Basically, you want to play in a game for as long as you have an edge or until you find another game with a better edge. There is no reason why you should leave after you win money if you still have an edge over the other players. My gut instinct tells me that you have only been winning early on after sitting at a table and later losing because of variance. If you played alot more you would find that you lose just as much early on as latter.

If this is not the case then there could be a very large leak in your game. I would advise fixing the leak instead of trying to constantly change tables. If you are losing more after sitting at a table for awhile then you either have a very transparent way of playing or you are not paying enough attention to the other players. You should learn to analyze other player's games or get a program like game time + to do it for you.

Some multi-tablers feel that it's a good idea to change tables every once in awhile because they are not paying as much attention to individual tables as much as a player playing just one. I think they would be better off getting game time + because that way they can play multiple tables and at the same time have adequate knowledge of their opponent's game.

There are a few profitable hit and run styles that only work by changing tables frequently. Also, if you are ultra rockish and you don't want to loosen up then it might be a good idea to change tables frequently and have multiple usernames so you won't get pegged as a rock.