Good recruiters are basically your sales force. They'll be out there building connections and holding a very wide book of open opportunities for you the moment you need them.
The good ones will also be respected on the other side, by the employer. If they think you are a particularly good fit for a good role, they can have both you and the employer walking into a very warm lead before you even start your search.
I have two or three recruiters who have kept me busy for a decade. I tend to think of them as partners as much as anything. They know I won't make them look stupid in front of their clients, and I know they will do the right thing by me by being frank & honest.
As with all professions, some are better than others. However, if you treat all recruiters with disdain you are also damaging your own prospects in terms of building some potentially mutually rewarding relationships.