It's not so much that it "makes sense", but that you need it to comply with CAM SPAM.
Any unsolicited mail must have an unsubscribe link, even if you just email them once.
Any unsolicited mail must have an unsubscribe link, even if you just email them once.
The reason for this is really for mass emails. It really should not apply when you send a few hand-written emails to a few people.
I thought it was a typo the first time you typed it, but I thought you should know when I saw it a second time.