Can/should the same registration account be used on multiple servers?

Can or should the same registration account be used on more than one server?

If so, is it simply a matter of registering the same email address when running the client for the first time on each server?

I can answer the question of “can” - yes, as I’ve done it, and yes I just used the same email when running the client for the first time on each server. As to the “should”, I don’t know any reason why not …