At this point, most professionals have a LinkedIn profile. However, a good amount of them are not very detailed. LinkedIn is a great platform for networking with professionals AND is a great place to find a new career or be contacted for opportunities you may not have known about otherwise.
Just simply having a LinkedIn profile will not get you contacted by potential employers. It is very important to put as much detailed information on your LinkedIn profile as possible. From a recruiter/employer standpoint our searches will be keyword, experience, and skills driven. So the more information pertaining to what you do and what skills you have obtained, the better the chances of coming up in the appropriate searches and being reached out to for potential career opportunities. That being said you should still always have a resume besides your LinkedIn profile at the ready.
If you are not looking for a new job or interested in hearing about them, it is still a good idea to keep your LinkedIn profile updated. LinkedIn has made it easy so you can simply decline an inmail from a potential employer or make it where you do not accept inmails if you are not in the job search mode.
Overall, LinkedIn has become an important tool for not only employers but job seekers as well. Sometimes the best opportunities surface when you are not even looking!