I'm a perfectionist and am perpetually unsatisfied with my save files. I currently have one legacy going in a save of its own and fight the urge to restart it daily. I am usually working on a template save as well--a save with everything made over. Even that isn't enough because sometimes I want to play with pre-made townies and sometimes I don't so I need different template saves based on that.
There's also the fact that I like to replace all the builds with things downloaded from the gallery. Every time I think I've found the ideal download for each lot, I find something I like better. Rather than going through all my saves and replacing the lots it's almost easier to just bulldoze all my saves and start from scratch yet again. Same thing with CAS. Every time the game is updated to round out sims even more, I want to start from scratch and edit my townies with the new options.
I wish I wasn't like this, it would make my gameplay more satisfying, but I don't think I'll be able to have a longstanding save until the game is completely done releasing DLC/updating.