Facebook has killed my friend email archive
Up until recently, most interactions with friends were over email or text. Both of which are easily archivable. But since everyone went onto Facebook people have been largely communicating on Facebook so now I don't have a full archive of communications any more.
You might think that this doesn't really matter, but sometimes there are occasions when it's helpful. It's helpful for trivial things like finding other people's email addresses that you need to get in touch with. But it's also helpful for more serious things like grieving. Having an extensive archive on your computer of conversations with people that have died can be therapeutic. You can quickly flick through and find their funny stories and photos without having to rely on still being able to access Facebook (and assuming Facebook don't start deleting old accounts and messages.