People use password managers so they can conveniently have a single password without a single breach compromising all of their accounts.

This is the same idea but for their email identity.

Here's a fun one: https://www.martinvigo.com/email2phonenumber/

The more places you use the same email address, the greater your exposure.

If you are privacy conscious, yes. Compartmentalizing emails used for services is useful. It also tells you who is selling your information.

Also, when it is clear someone is abusing the email you provided, you can nuke it. Perhaps some functionality to be had here between aliases and haveibeenpwned detecting an alias in a breach, queuing for alias cycling or invalidation with a human approval step.

If one address is getting spam I can just turn it off or filter it to the trash.