I find myself not wanting to throw away paint when there is a substantial amount left as I have just reached a plateau of a piece in which I am working. Oils you can revisit but Acrylic your time is brief.
Just as my Tutor when I was in 3rd grade said….. always comes to mind. There are no mistakes in art.
I had dropped my brush with a dot of red in the middle of an ocean scene with a boat. She very quickly picked up my brush & created a tiny flag on the mast.
I look at my leftover paint, not wanting to waste it & quickly whip out something unplanned. Sometimes it turns out very well