👋 Hiya Simon!
Great question!
I've seen a variety of perspectives.
Personally, I saw someone post a long while back something along the lines of "Go ahead, give a favorite post of yours a boost. Since things here are [mostly] not driven by an algorithm, and followers may span many, many time zones, it might help get your cool toot in front of someone who appreciates it." And that's been my MO.
Other folk don't care for that practice.
Mastodon lets you control whether or not the boosts of someone you follow show up in your feed (on a per-user basis), fwiw.
CC @TheBreadmonkey , fellow self-booster.