One of the things that can cause a crash on the sims 3 is video card overheating, worse, this overheating could damage your videocard or even computer. The curious thing about this problem on the sims 3 is that it can happen even if your videocard exceeds the system requirements by far, in fact, it's more likely to happen if that's the case.
Why does the sims 3 overheats your very expensive new videocard?
On most games, if your videocard is far more powerful than what the game requires, it doesn't have to work as hard to display the game and thus it runs cool. The closer the card is to the minimal system requirements, the more effort it needs to run it and thus it runs hotter.
This is not the case for the sims 3: while the sims 3's engine is internally locked to run at 30 frames per second (fps from now on), the game haves absolutely no limit on it, so the game cranks out your very expensive new videocard for all it gives, producing ridiculous amounts of identical frames each second (it was running at 3000 fps in my case) and thus overheating your card.
This problem is of particular concern to laptop users (at least for new laptops) or those who's computer lack proper ventilation.
So if your computer is slow/old, you're probably not having this problem, but if it's fairly new and you're noticing that your computer is running far hotter than what it should while playing, you may want to use an external application to force the sims 3 to run at 30 fps (and thus protecting your new expensive video card from turning into a new expensive and charred paperweight).
UPDATE: If you are unable or unwilling to find a third party program to limit the game's fps, another method of enforcing an fps cap is to force vsync on your videocard control panel, this will force the game into running at 60 fps (or whatever the refresh rate of your monitor). You'd still be wastefully rendering twice as much frames as needed, but your game won't hit silly high fps numbers either, so it's healthier for your computer.
Expect to have your computer running cooler and more silent while playing if you do either, particularly during load screens.