It's usually best to merge duplicate entities (releases, release groups, recordings, etc.) instead of deleting them.
Deleting entities has two kinds of bad effects on the database:
- The MusicBrainz identifiers that have been referenced anywhere (tagged files, links to MusicBrainz from other sites) will become invalid when the entity is deleted. When merging it, however, the old identifiers will forward to the entity it is merged into.
- Even if there's no useful data attached to the entity when you enter the edit, it's possible that someone may enter it before your removal is approved. If so, the recently added data will be lost.
For similar reasons, it is better to merge misspelled artists into their correct names, instead of just moving their releases and/or recordings to the right artist and let ModBot remove them. This also adds the misspelled version as an alias for the artist, which makes more unlikely that the wrong name will be recreated.
As a general principle, if you can solve an issue with non-destructive edits, that's preferable to a removal.
For instructions on how to merge releases, see this how-to.