Can't say my Sims 3 game is volatile, since I have been playing the same family for seven and a half years now (I'm in generation 21 at the moment). If anything I'd say on the contrary, Sims 3 enables me to still have every heir I ever played in my game (on the graveyard), which for me adds a lot of depth to the experience. And my world is filled with family members of my current heir.
Sims 3 can have its whims though, so it's a good idea to take some measures. I see you already got a lot of advice concerning mods and mods are great, but I must also add (after playing the game vanilla for years) it can actually be mods that make your game more sensitive/fragile. Ever since I use them I have occasional crashes, something that hardly happened before. This is not me being anti mods; the mods - and CC - I have now I wouldn't want to miss anymore, but it is a warning to be aware of that and not stuff your game with them. I often see mods presented as a solution, where I can't help wondering if they might in fact be part of the problem in some cases.
Though I hardly suffered from actual crashes when playing vanilla (I was not familiar with 'Sims 3 has stopped working', nor with the infamous error code 12), Sims 3 does come with save breaking bugs. Which is why I learned to 'save as' and number my files. That way, whenever things do go wrong, you can always return to an earlier save. Another thing I always do is saving my family on a regular basis (to MediaFire).
When you do use mods (and honestly, I can recommend them and in some worlds you'll have to because they have severe routing issues only NRaas mods will solve), you'll have to make sure to clean your cache files before playing (the ones @lisasc360 mentions). And whenever your game does crash, make sure to empty the currentgame folder before restarting the game.
Sims 3 is delicate, but also quite user friendly where it comes to saving the game, sims, families and houses. Which in my view makes it anything but a volatile game, as long as you take precautions.