If only people got more prize money for faster checkmates, or they mattered in any way shape or form!
When is it better to underpromote?
Fast mates score 1 point in chess games. Slow mates score 1 point in chess games.
Fast mates score 1 point in problems. Slow mates score 0 points in problems.
See the difference?

The difference implies problems are spurious since games are what matter!
Truth matters. Games exist only so that you can develop your vision for problems.

just s/t i wanted2say. i feel its mean (cheeky) to underpromote in a totally won game. just getta Q for gawts sake !

just s/t i wanted2say. i feel its mean (cheeky) to underpromote in a totally won game. just getta Q for gawts sake !
When it's past time to resign, cheeky is what you get.

Promoting to Bishops just for the sake of it isn't 'better to underpromote' though. It's just choosing to make a game last longer!

The only time I've ever had occasion to underpromote to a knight in a game wasn't to give check -- it was to *avoid* getting checked:
I was about to resign, when I noticed b8=N!
I wish I could report that I managed to hold the draw, but even with the underpromotion, I couldn't quite save it. Still, it bought me an extra ten or twenty moves.
Have had a good look at that game you laid out in that post: https://www.chess.com/a/NcGHkSSJy7gi
and I think I understand the situation, can I just check: you were hoping to stay out of harms way for 50 more moves? Is that the basic idea, the best you could realistically hope for in that position?
Why not post #66 as puzzles, RewanDemontay? They are nice problems!
They aren’t really meant to be problems so much so as economy attempts.