Greeting Sizzlers,
If your using TB, then you have to be rooted. In my experiences, just saving the apps keeps a record of your in game progress. When I restore, I just batch restore all apps with data.
If you are messing with custom roms and such, restoring system data across different roms could cause you a lot of headaches. That means if your made a back up under rom A, and then switch to rom B, restoring your system data backup will overwrite rom B with rom A information.
As far as overwriting you back-ups, there is a option in TB that allows you to set how many versions you wish to save before overwriting takes place.
1. Menu button
2. Preferences
3. max backup history
Hope this helps.