@kjoo I do it sometimes, its been a thing people do for as long as I have been here (~5 years now.) I've considered it generally acceptable so long as it's not spammy.
I have people who follow me from multiple timezones so sometimes I will boost a post so those 12hrs a way will get a chance to see it, usually for polls, or questions I'd like answers to.
For older content, if it's good i'll boost it days, weeks or even months afterwards. Often just as a: "I want to say this again."
@kjoo I try to silo my content among different accounts, sometimes I will boost my content between accounts because I feel it's maybe interesting to the people following me elsewhere.
Boosts are how posts move throughout the fediverse, self-favouriting doesn't really do anything as far as I am aware.
@kjoo @carbontwelve I use it pretty much exactly in Mx Autumn's way!