The Facebook and the Linkedin both have their own benefits. I want to describe both the sites in a positive way with limited limitations.
Facebook is a social site in which one can have an account to share their personal life moments and keep update their friends and families from being anywhere and anytime. It’s more like fun. One can have leisure time to spend on this social media site. They can post their status to let people know about their moment. I am using Facebook for almost 11 years. Generally, I don’t post much about my personal life and moments because of the privacy and security reasons. So, people must be aware of the use of this social media site if they use it without knowledge then how bad it may lead to them. But its used with limited access then it’s more like social fun. Generally, I post pics, Occasional status and some good stories but not more than that.
However, on the other hand, LinkedIn is a most professional website. Which is in high demand nowadays for professional network and connections worldwide to build a career. Not necessarily most of the professionals and higher officials would be using facebook but you can find them on LinkedIn for sure. I am using LinkedIn for more than 8 years and it has benefited me to build my career by making international connections. In the beginning, I was using it to search for jobs but then I started looking for international connections to go abroad and I found the position now where I am. I would advise you to start building your network on LinkedIn rather spending or wasting your time on facebook. This will help you to get a job as soon as you finish your graduation or to find another good job better than presently you are working. Most importantly you can stay updated with the latest research going on through article shared by your professional connections.
Overall, I would say LinkedIn is more important to build your career, whereas Facebook is waste of time. So moral of the story as per experience is there is no obligation to use Facebook but prioritize your goal and then you can have time to use or spend your leisure time on Facebook.