Those sound like tools for very immediate, personal attention. Facebook allows for that (like messaging or writing on someone else's timeline directly), plus a bunch of intermediate levels. For example I can post 200 photos from my vacation in an album, and it just shows up as a single item in my friends' timelines. Any of my contacts can browse it if they want, but it doesn't take up disk space in their inboxes, they can start a conversation connected to any individual photo, and it's not as insistent as if I'd sent them in an email. And if I really want someone to see it, I can tag them or just message them with the link.

Facebook also serves as an auto-updated contact list. If I update my email or phone number, many of my contacts won't have the new information. FB doesn't have that problem. In fact I can put my phone number and email on my FB profile and my contacts can optionally auto-sync that info right to their phones so it is always up-to-date. It's possible to be "friends" with someone but not "follow" them so you don't see their posts in your normal timeline but you still get their contact info. You can also make closed or open groups which are helpful for event planning and multicast messages, and "friend lists" which let you customize the reach of each post. I guess you could do that last one with email too.