If you are already subscribed to a CiviMail group, but then revisit the subscription page and try to resubscribe to a group, you get the same subscription and welcome emails. Would be nice to do 1 of the following instead:
1.Have screen alert you that you're already subscribed after you enter in your email address (seems preferrable)
2. Instead of sending subscription request/welcome email send an email that says "you're already subscribed".