E.g. types that are unlikely for the medium formats of the release or types that make not much sense in combination.

Examples

• https://musicbrainz.org/edit/84447399 (too many types to count, ticking all the boxes)
  • https://musicbrainz.org/edit/92952654
• https://musicbrainz.org/edit/90057885
• https://chatlogs.metabrainz.org/brainzbot/musicbrainz/msg/4727219/ (liner on non-CD release)
  • https://musicbrainz.org/collection/66eb6c0d-ed66-4eaf-8e2b-b6e3751cb2a5
• https://musicbrainz.org/edit/89132164 (back+tray)
  • https://musicbrainz.org/edit/92386880
• https://musicbrainz.org/edit/90547964 (medium+spine)
• https://musicbrainz.org/edit/90960528 (track on physical release)
  • https://musicbrainz.org/edit/91139964
• https://musicbrainz.org/edit/92378554 (back+booklet)
• https://musicbrainz.org/edit/93071969 (top, medium on digital release)
• https://musicbrainz.org/edit/97464612 (front+tray)
• https://musicbrainz.org/edit/97464613 (front+medium)
• https://musicbrainz.org/edit/97464615 (back+medium)
• https://musicbrainz.org/edit/109541609 (medium+top/bottom)
• Especially for vinyl often medium is combined with front or back so it's displayed in the sidebar, see also MBS-4650

For further inspiration see also the "Supercharged cover art edits" userscript