The function user_delete in functions_user.php does not delete poll votes, as previously reported here: https://tracker.phpbb.com/browse/PHPBB3-9838

While that was closed as "won't fix", anonymizing poll vote user IDs and especially IP addresses should still be done.

Similarly, posts and PMs retained after user deletion still keep IP addresses.

Users often request account deletion out of privacy concerns. It is reasonable for users and board administrators to expect that user deletion removes all personal data that can be removed automatically.

Especially when retaining posts under their original username, having IP addresses associated with those posts can be a privacy concern.