Why install postfix?

I’m curious as to why:

ee stack install --web

…installs postfix? Isn’t the point of this specific command to only install necessary web packages?

Additionally, why is it running, by default?

Example shown in attached image:

Postfix is needed for sending emails from websites.

--web stack is most commonly used by WordPress sites.

Ok, so the php mail() function requires Postfix?

With all the delivery/sending options for email, people still use that?