It keeps phishing attacks from being able to cross services (since if you get a citibank email to your coinbase email that would be a big flag) and it reduces the attack surface on other sites.
I use [email protected] for this purpose and it makes it handy to see who has somehow lost/disclosed my email to third parties and not informed me (FreshDirect for example)
I use [email protected] for this purpose and it makes it handy to see who has somehow lost/disclosed my email to third parties and not informed me (FreshDirect for example)