What is Facebook for is a pretty good question. It causes a lot of head scratching to work out an answer to that one. When it was originally started, it was a social network that people in college could use to talk to each other from their lodgings. Facebook them morphed and became bigger and as it became bigger and more convoluted, its purpose became ever less clear. Generally, it seems to be some kind of play area for children, teens and adults of all ages with postings ranging from the absurd to the obscene. It seems more to be a combination of a messenger program and a bulletin board program with a few bizarre extras thrown in.
Facebook is a double-edged sword. Many people will use Facebook under their real name and place photographs of themselves on Facebook. This can lead to employers looking to see who is there that has just applied to them for a position. Generally the best thing seems to be to have a profile under a nom-de-plume and to delete the profile once a year in order to start afresh. That way, all the updates that might be embarrassing vanish in one fell swoop.
A good way to think about Facebook is "if this was written on a noticeboard at work, would it be embarrassing"? If the answer is affirmative then the resolution would be not to put it on Facebook. Private and hidden data on Facebook has had an awful tendency to be revealed in the past. Indeed there are many lawyers that love Facebook. One lawyer was reported to say that work as a divorce attorney was so much easier with Facebook because the other party would frequently have a photograph with a paramour on a beach instead of being at a business conference.
Is Facebook worthwhile for a photographer? Maybe, maybe not. The big turn off about Facebook is that Facebook tends to be very casual about using photographs posted by users in their own advertising, without crediting the user. On the other hand, since photography is not a real job, does it really matter anyway. Nobody is likely to have ever paid for the photographs in the first place. Some photographers do use Facebook to drum up the small bit of business that photography gets though never enough to live on and certainly not often enough to consider turning it into a business.
For the job-hunter, perhaps deleting one's Facebook and LinkedIn profiles are a smart move. That way nothing can ever be held against the job-hunter. Indeed, it could well be worth just deleting all online accounts so that nothing could be held against the job-hunter in search of work. Recruiting officers have some very strange ideas so a complete web absence could be beneficial.
On the whole, Facebook probably has more downsides to upsides. There are the messages posted that could be embarrassing in the cold light of day, the messages that future employers won't like to see and the messages that might be upsetting to those looking for a reason to be upset. There are plenty people like that around!