It depends on whether you want the user.app_metadata and user.user_metadata appended to your access token/ID token. If you do not intend to use the information after decoding the access token/ID token, then it will not be necessary to include them.
On the contrary, if you intend to use the user_metadata or app_metadata for some logic, I recommend appending the user_metadata and app_metadata as custom claims to your tokens.
In short, you will only need namespaced custom claims if you intend to append them to an access token or ID token.
I hope that helps clarifies your questions.
Please let me know if you have any additional questions. I’d be happy to help.