If a group has become redundant, you can remove it from Jira:

1. Browse to the Group Browser page
2. Click on the Delete link for the group you wish to remove, and click on Delete again to permanently remove the group

Once you remove the group, all the users who previously belonged to it will have their group associations updated to reflect the change. However, if you have other configurations using the group, it can have a negative impact if you are not careful. For example, if you are restricting the Create Issue project permission to only a group called developers in your permission scheme, by deleting the developers group, nobody will be able to create issues in the projects using the permission scheme.