what is the benefit of having a bogus email account ?

Essentially, when you sign up for a service or list or anything like those, there should be an expectation that the company will sell your email address.

With Hide My Email, you can set a single email address for each one. When you start getting spam from other sources than what you set it up for, you know that company isn’t trustworthy and you can cancel your account with them and disable the email address.

Learn more about Hide My Email and iCloud+

It is not an email account, but a email address alias which forwards to your actual email account. It is not bogus as it is a real email address. Hide My Email will create random email address alias for your real email address. Think of it as a nickname that changes depending on who you talk to. :)