LinkedIn is one of many ways a recruiter can keep you informed of what is happening in your industry and let you know which companies are hiring and which are downsizing. It is a vehicle to let you know what job opportunities may be worth exploring.
Most individuals accept the messages received from recruiters re job opportunities; some respond and are interested, some send referrals, some just read and say thanks while other's will just delete them. All that is fine. But every now and then a message will be returned stating that the message was appropriate but not at this time and declined by the individual. Why decline? It was appropriate. There is no need to decline. It sends a very negative message to the recruiter. There may be a time when you need a recruiter due to an unexpected downsize or life changing event and I trust you wouldn't want to be declined. Just a thoughtful bit of networking advice.