Those of us using a different random username and/or email address for each sender do it for two reasons:
1. If whichever identifier is used for login (eg. email address) is exposed/leaked, it cannot be used by the attacker to lookup accounts in other leak dumps.
2. It allows to detect which site/service/entity is selling or leaking email addresses to third parties which send spam. I no longer need or have a spam folder. The moment I receive a spam email from someone I don't recognize, I can lookup which site/service that email was for, and choose how to act; eg. update that site/service's to use a new email address and blackhole the old one; maybe unsubscribe/close the offending account if it happens again. Of course since setting up my unique-email-per-site setup, I haven't been victim to third-party spam yet; likely because I no longer have a personal email in public Github commits.
1. If whichever identifier is used for login (eg. email address) is exposed/leaked, it cannot be used by the attacker to lookup accounts in other leak dumps.
2. It allows to detect which site/service/entity is selling or leaking email addresses to third parties which send spam. I no longer need or have a spam folder. The moment I receive a spam email from someone I don't recognize, I can lookup which site/service that email was for, and choose how to act; eg. update that site/service's to use a new email address and blackhole the old one; maybe unsubscribe/close the offending account if it happens again. Of course since setting up my unique-email-per-site setup, I haven't been victim to third-party spam yet; likely because I no longer have a personal email in public Github commits.