In building out a customer support team, tech support team etc, each of which contains multiple people on a team, we really need to be able to select from a list of send-as or "from" email addresses.
If we have 5 people on the tech support team for example, all of them should use support@yourdomain.com, but have their own dynamic email signatures.
Similarly, if that same person is also on the client support team, they should all be sending and receiving email at info@yourdomain.com, which changes that persons signature since they are acting as a different role within the business.