> I just let the migration assistant do the needful

but will it revert back if things go wrong?

It leaves the "source computer" alone, so if it blows up you can always just start again.

I never trade in my old computer, even if I'm going to sell or get rid of it (donate) I keep it around for a month or so to make sure everything's working.

It reverts back and it does it at its earliest.

Dear, this was gold.

I get that. Personally, I'm a bit weird because I don't like to bring all the stuff from the previous machine (documents, files, etc.). I like to start fresh and only install a couple of apps / configure some settings.

Understandable - it gives you a chance to do "spring cleaning" and decide what you really want/use.

Exactly, haha. If something's important enough, it'll find its way to the new machine. :-D