Good point!
Why do they need my profile URL? What's the purpose? Thanks in advance.
Usually someone needs your profile URL when they are accepting you in some kind of signature campaign or bounty which is paid in Airdrops. This is for them to find who participant in that signature or bounty has such posts , quality of posts and all the related data regarding such project. This is also needed when you join a signature campaign which is paid in bitcoin and is common procedure when applying for such signatures.