Recruiters often find potentially interesting profiles and are sending connection requests. They do that usually to send job offer.
Having a lot of recruiters in contacts is especially good idea for freelancers and contractors specializing in short-term contracts. You can easily send signal that you are free now or your project is about to change now and you are open to new opportunities.
It isn't guaranteed to succeed, but many people have found contracts using LinkedIn, and filling profile costs you little effort, so it's worth doing.