Don't you mean the other way around? I wouldn't be adding dbo permissions if your application is working without them - it just creates an uncessary security hole.

I have seen a number of instances where dbo permissions were added as a quick work around for a permissions issue and never removed, so I agree that it is a good thing to check for. If you can spare the time to audit what permissions the login actually needs, it is by far preferable to work out how to remove dbo. It could even be essential depending on the security profile of the system.