With regard to King Crimson specifically, Bill Bruford wrote some interesting remarks in his biography about UK progressive rock striving towards a Gesamtkuntsw

With regard to King Crimson specifically, Bill Bruford wrote some interesting remarks in his biography about UK progressive rock striving towards a Gesamtkuntswerk where the cover design was a key element alongside the music. I’m a sucker for inventive sleeve design myself, and my all-time favourite for that is the record label 4AD in the 1980s and 1990s. That label’s in-house design firm 23 Envelope/v23 produced covers that really complemented the music, and have even been exhibited in art museums separate from the music. At the same time, there were a few artists signed to 4AD who resented somebody else’s art appearing on their records, regardless of how appealing fans or potential buyers might find it.