I have never started from a save, I always start from scratch, because sometimes they add new things or improve some renders or I make different decisions.
I have a short memory so I start again every time. even if afterwards I end up remembering I have to start all over again since I overwrote the previous save
From save unless the game has some really good storytelling (games made by Oceanlab or Naughty Fox Games for example). Also a lot of RenPy devs fuck up the save files and you are forced to start from scratch either way.
I always keep multiple saves with different routes especially if the game is made in rpgmaker but sometimes i have to roll back a litle if the story gets too confused.