Basically games that have their save files in the userdata folder. Let's say for example I install a new game and save, if I reinstall it, depending on the game, it might not recognize my saves at all even though they're physically there in the appropriate folder. For the longest time, I used to think this is a side effect of having Steam Cloud off and unknowingly overwrote my saves with a new save. The severity of this varies too. Not every game has this issue, it's just that as time goes on, there are more games that are affected than those that aren't.

If you're here to find a true fix for this, I haven't been able to find it. In fact, I can't even find anyone that has this exact same issue. Steam Cloud does not help. Here's a workaround though:

1. Copy the game's save files from the its userdata folder before reinstalling
   
2. If the game does not recognize any saves, usually rebooting Steam will make the game read some files or none
   
3. When that happens, paste the save files again onto the same folder. For some reason, doing that completely solves the issue and now the game will happily read all of your save files even though they're the EXACT same