HN is a good example of a different tradeoff. It uses usernames and usernames can be anonymous. Email is optional on the user profile. Not providing it means:

1. the feature of password recovery/reset is unavailable.

2. other users won't be able to directly contact you via email (and therefore this prioritizes privacy over other features/functionality).

As others have suggested, you can use the email for sending a context specific magic link for signin/registration completion.