I think they are pretty useful. Especially when you use them to filter out by checking (-).
For example, if you are looking for games that play with 7 people but you don't want to see party games. Or a game about animals, but not a children's game. Or games set in ancient Rome, but not wargames.
I never look at the Type and Category fields, my eyes are just not drawn there.
What I do look at all the time is the Mechanism field. That's one of the first things I check when finding out about a game for the first time. I also use that field extensively in searches. It's fun to do an advanced search for combinations of different mechanisms. For example what are some co-op trick-taking games besides Crew and Fox in the Forest Duet?
Yeah, mechanism is a lot more objective way to classify board games. We can argue all day about, say, what exactly a wargame is, but what games have hex grids, area control, and resource managements is a lot easier to agree on.
They are useful in combinations. For example, maybe you want a wargame that isn't also flagged thematic and that has bag drawing as a mechanism. Or you want a party game that is strategic and uses drafting. Etc etc.
What are family games? In regards to your question, i honestly don't use categories a lot in BGG, but the few times i did, it was useful.
Family games are defined as games that young children and adults can enjoy. For example, Crokinole.
In practice, this category is used for "gateway" games, like Carcassonne.
Everything boardgames
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