Was listening to pga radio K and Mc and they mentioned a major provides a 5 year exemption while a regular tour win two years (20 wins lifetime exemption). Plus the money plus the world and fedex points (at least in the modern era)
Seems they are somewhat important
I have played two of them and had two very different experiences. Old Works in Anaconda, MT was a joy to play. I played it several years ago so I don't remember too many specifics, but I do recall really enjoying the layout of the course and my playing partners also raved. The Idaho Club in Sandpoint, ID, however was nothing short of goofy. It was a decent small-town public course called Hidden Lakes at one point, until Nicklaus was brought in by a wealthy developer to redesign it. The result was a course that was virtually unplayable because of how difficult it was. The greens were absolutely ridiculous (4-putt city). I believe it has been closed down in recent years, and I understand why. You'd be hard pressed to find many golfers that enjoy inflicting that type of punishment on themselves.
I have played a few Arnold Palmer tracks as well, and his seem to be a lot more player-friendly than Nicklaus' courses.