Or, another way to describe: Copy an existing credential
It is very common to me create a new account in a site where I already have an account. So, I just want to create a new credential using almost all data I already put in an existing credential. Then change (almost) only username and password.
It may be implemented as a “copy” feature/button when editing a credential.
(it seems so obvious to me that I doubt that no one did asked it yet… I searched for it, but if it was requested before I apologise)