My game seldom crashed in Sims3 but I had hard copy of all the packs so wasn't online. However, it did crash occasionally. So I've been trying to see what's causing it now and I have found:
1. If I'm selling from inventory I can only do this a couple of times before it crashes. So I sell about 3 items, save, sell, save so I don't lose as much if and when it crashes.
2. If I'm moving things from inventory to the fridge, (or elsewhere but most commonly the fridge), it will crash after moving a few. Same as above, move, save, move, save.
3. When in build/buy mode if I do things too quickly or try to move things serially it will crash.
4. When in map view if I shift from one neighborhood to another too many times or too quickly it will crash.
5. Traveling often causes crashes.
6. Using testingcheats on is a guaranteed crash after a few minutes of play, but if I do testingcheats on, do my action, (fill needs usually), and then type testingcheats off it's ok. So cheating is a big no no in my game.
Just queuing up a lot of actions with my Sims seems to be ok. I can fill all three family members lists with actions, unpause, and let them do it without a crash. It's been pretty trying, trying to figure out what not to do to avoid repeated crashes. I can now play for around an hour straight without a crash but I'm definitely being much more careful and always am "saving as".