I've been doing a lot of categorisation lately, mostly filling up all the old UK television programme categories that I found woefully underpopulated, with (mostly) British actors of the era.
If I find an actor who was in a show, I look to see what other shows they were in and add them, and they default to the top of the page. In most cases I just leave it at that and move on, though I might take a bit more care if it is a carefully curated profile with lots of categories and details. Like an architect designing an extension to an old building, you try to follow the same style. At the other extreme if there is no information at all I might add a little one-line summary and a Wikitree/IMDB link.
I don't think too many Wikitreers overly concern themselves with categories, they are kind of an afterthought and I guess it's up to the profile manager, if there is one, to arrange the order. It's more of a presentation issue, like putting backgrounds and photos on a profile. Many profiles don't have any categories at all (and I'm as guilty as anyone when I'm building a chain of profiles to connect someone to the Big Tree).