The Interactive Fiction (IF) cruelty scale

The cruelty scale is one measure of how difficult a developer has made a game based on how many saves the player has to keep and how obvious it is that they should make a save. The original scale has five ratings: Merciful, Polite, Tough, Nasty, and Cruel. This is not a measure of how hard a game might be.
See IF Wiki: Cruelty scale  and TV Tropes: Unwinnable by design 

Ren'Py features a limited undo feature (roll-back) that allows the player to go back and revisit previous choices and explore different paths as well as a large number of save slots. Players expect this of Ren'Py games and this allows games to verge on the nasty because you can go back and make a save before your unfortunate choice.

Developing a game that disables the roll-back feature (except where technically necessary) or limits or wipes the player's save games is only likely to annoy players.