As Chris says, if you want to make money out of photography and sell prints, it is a powerful tool, or can be if done well.
As much as one might dislike social networking platforms, they are increasingly influential. If one has professional aspirations and is starting out now, it is worth getting on board. For well established photographers it is less of an issue as the building of that business took place in a different era. Sounds silly, but today and ten years ago were very different eras in some respects.
As for plagiarism of images and usage by FB, you do not lose the rights to those images, only FB has the right to monkey with them. Personally, I am not that bothered if they monkey with a 450 pixel image, if I get to sell a 40" print for very good money, or my promotions get people along to exhibitions where they do so. I think it is a case of weighing up the greater benefit.
FB claims that these measures they put in place were intended to prevent law suits resulting from internal use. It does leave all FB users vulnerable to having their content sold on, but I am not aware of any examples of FB selling on images for commercial purposes or using them in this manner. Do such examples exist? If they do, then it is a different matter, but it seems widespread fears have not been substantiated. Yet.
This might also be helpful as one pro wildlife photographer put this issue to FB
https://www.facebook.com/note.php?note_id=270204724175
I started one a while ago and have not pushed it yet, but I get regular hits on my website from FB traffic and they comprise a decent percentage of the total.
If you want to do photography as a business, a facebook page is worth the time. I've sold many prints to my fans. Does take a while to build up a large fan base though. I have 466 fans, but it took 3 yrs to build that many, but It really isn't that much work.