LinkedIn is a site I love to visit everyday, although it may not be as big as Twitter or Facebook but it sure caters for the people in the business community who want to use social media to promote their business.
Your linkedin profile shows people your resume.It is perfect for showing people your skills,experience and so on.You may get hired by top companies if you have the skills and experience they want.
Others can recommend you and endorse you.The good thing about that is anyone who sees your profile can see this .It shows you have experts backing up your claims.This allows you to make connections.
You can also show up your projects and completed works on LinkedIn and people will contact you .
If you have a website,you can use LinkedIn to get traffic to your website. If people love your content or what they see on your profile,,they will click on your link and visit your website.
Their are some other benefits which I won't want to dive into like building relationships(people in your career path you can seek advice from,getting connected and so on)