iMessage drives me bonkers since it insists on giving previews when sending. If I see something funny on YouTube and I want to send a link to "10 seconds ago", then I can't just go to "copy URL at current time", paste it into iMessage and fiddle the time code back 10 seconds. Instead I need to paste into something like TextEdit, edit the code there, then copy it again and paste that. It's a usability nightmare.
I might also be sending URLs with tracking codes and stuff on them, since I can't see what I'm sending.