First, technically what's going on. Let's start with Bob and Joe. Let's say that Bob blocks Joe:
Blocking someone is basically making them disappear. If Bob blocks Joe, then Joe never sees Bob.
Bob goes to his face book page and in the upper right corner is an icon for privacy short cuts. Clicks on that and one of the options is "How Can I Stop Someone from Bothering Me?". Click on this and Bob gets a search box: type in Joe's name or email, get a list of 'Joe's, pick the one and he's blocked.
Bob can also block Joe by going to Joe's page, and next to the Message button in the upper right of the page, click on the "..." and there's an option to block.
Blocking will unfriend someone. Unfriending someone does not block them.
There is a short time period between when Bob blocks Joe that Joe will see an odd page. I've see where the blockers page flashes up briefly and is then replaced with a error message "Sorry, this page isn't available".After a couple days, Joe will not see anything from Bob. If Joe searches for Bob in FB, Bob won't even come up in the search results.
Once Bob blocks Joe, Bob will not be able to add Joe as a friend. Bob would need to unblock Joe, then send a friend request and Joe would have to accept that request.
Joe will not know that Bob has blocked him - there is no notification. Joe will figure it out eventually, for example, if Bob posts a lot each day and then suddenly there are no more posts, Joe might think something is wrong.
There are ways that the blocked person can see the blocker - it doesn't make everything about the blocker disappear. For example, if the Joe goes to google and searches for Bob, and he's logged out of Facebook, he can see Bob's profile page. There are also some applications that can be added to Facebook that reveal information.
There is a way to prevent search engines like Google from displaying your profile information, just go into the privacy icon in the upper right, click on 'see more settings', then click on 'Do you want search engines outside Facebook...' and turn it off. Of course that old high school buddy won't be able to find you, but maybe that's okay.
If Bob and Joe have had a conversation in Messenger, that conversation will still be there. Not sure about this, but Joe might be able to continue the dialog in Messenger as long as Bob doesn't leave or delete the conversation.
Why block someone?
The first and obvious answer is that blocking is for stalkers, bullies, harassment, prostitutes trying to hit on you, and annoying sales people.
Blocking seems to be something that teenagers do when they're 'mad' at each other. There can be an immature side of blocking, 'I'll teach you' kind of thing.
There can be legal situations where Bob doesn't want Joe to see what Bob is doing because there's some legal issue between the two of them or Joe is party to someone else who is in a legal conflict with Bob. This seems a little odd in that: why is Bob posting things that could be used in a legal situation?
Unfriending is a kind of parting of the ways: maybe they have drifted apart. Maybe it's someone you don't really know that well and really aren't interested in what they post. I got unfriended once because of some moral position I expressed. Unfriending leaves the door open for future contact. Blocking says "I don't ever want to see you again".
There may be confusion about unfriending and blocking. Maybe Bob didn't realize he had options and just reached for blocking because that's what he last heard.
Technically, blocking makes the person disappear. That's pretty strong. In social relationships, saying, "I want you to disappear" is serious. If I'm that evil person, then there may be good cause. But if Bob and Joe are just having a rough patch and Bob blocks Joe, that seems out of proportion - maybe they should be talking to clear things up rather than Bob just hiding behind the Facebook block.
Facebook is like a fun house mirror: we tend to think more people are watching than actually are, we think that the stuff we write is more important than it actually is, and maybe unfriending/blocking sends a message when it actually doesn't. Maybe the message it sends is that the blocker is just being trivial and immature. I believe that Facebook can be used to help build relationships and stay connected, but it's not a substitute for the real thing.
Bottom line: (1) use blocking for the serious cases, (2) if the relationship is in a rough spot, go talk, don't hide behind Facebook blocking.
