What Are Your "Bad Simming Behaviors"?

My main problem is starting off a save with one male sim and vowing to just let him get married and have two or three kids and just play his family and their generations alone.

I always end up instead populating the whole game with his offspring (wanting to see the mixing of the genes and who would give him nicer kids and which kids would look exactly like him and so on) so when they grow up they cannot find a mate because almost everyone is related. His family tree is also very over large and not wanting any of his kids to die childless I include too many townies and create new sims for them so eventually the worlds are too full and there is no where for new sims to go. So then I would put aging on short to kill off some of them naturally which also causes some of the ones I am playing with to die off without completing certain goals I had for them. So I eventually get overwhelmed with the game and start a fresh save vowing not to make my main sim the town rat again.

ETA - @ldmarko I also buy all the packs just because I just have to have all of the packs!!