There is no downside to using the explode mines scroll immediately. When shooting for max score of 365, it is best to plan to find and use the scroll so that you can trigger it immediately when you XP up to 10 hearts.
Very good - that is of course true!
In practice there is very little reason to not blow up the mines immediately when it becomes possible. This is because one has to do it before having to resort to the next health scroll (the XP from the mines is better), and at that point of the game, since one has >= 10 HP, then there are no things on the board that can kill the player at health. (only mimic chest, but it makes itself known on click) So ambiguities are not that important anymore.