A recent edit https://musicbrainz.org/edit/40528047 takes the view that many soundtracks (those that don’t have their own score but instead incorporate existing recordings) be tagged as compilations as well. My first reaction was of course not but on reflection the idea has merit. There are many examples of this kind of soundtrack (likely the majority; few movies produced these days can afford their own score).
One advantage to taking this approach is that it would allow us to distinguish these very common types of releases from an actual movie score, which has a style much like the classical style featuring composers and performers ( https://musicbrainz.org/doc/Style/Specific_types_of_releases/Soundtrack ).
I think it would be very useful to be able to clearly distinguish between these two types of releases, one with a composed score such as one of the Star Wars soundtracks https://musicbrainz.org/release-group/405fd3c5-0a45-456a-b853-6f734d3b57aa , which we could leave tagged as album+soundtrack, and the other being a movie that borrows existing recordings, often deliberately to establish a particular time and place like in American Graffiti https://musicbrainz.org/release-group/fb6ad135-7ee5-31d1-9885-bad0ce1025ce which would be tagged as album+soundtrack+compilation. We would need to explain this distinction in the style guidelines, of course, and there’s a ton of work to reclassify the soundtrack+compilation albums already in MB.