Prevent or minimize the chances of losing an important saved game by always using "Save As..." (or, at least, from time to time). This habit isn't only useful for Sims 4 but any game from the series or, even, any game or even office application!
We've recently had another important wave of corrupted Sims 4 Saves due to a bug with The Sims 4 For Rent Expansion Pack, therefore it's just timely to remind everybody that "Save As..." and "Backups" are always your friends. Not only with Sims 4 (or Sims 3) but any other game or even office application!
The Sims 3 "Save As..." Video Tutorial
The video above is very old but you might find it useful if you're playing with The Sims 3!