At the bottom of Apple’s share sheet on the Mac are the people you email the most recently (this menu appears in Safari and a number of other apps). They’re shortcuts to sharing the current webpage or document with those people about as quickly as possible.
It’s a little bit of a habit switch for me, but I really like it, at least for email. I thought Messages were included here, but I don’t see any right now, possibly because I’m testing El Capitan and maybe installing it reset that menu?