There are many situations which necessitate a change in permissions and even ownership of a folder.
If for some reason you no longer need to be an owner or collaborator on a folder, you can use the drop-down menu by your name to change your status.
If for example, you are no longer involved in a project, you may need to give ownership of the project-related folder to another person. This can only be done by the folder owner and once that person has already been invited as a collaborator(co-owner/editor/etc.). Changing a collaborator's role to 'owner' will grant them full ownership of a folder.