It's secondary to any other insurance you may have, including a personal liability rider on your homeowners. That doesn't mean you don't need it if you have homeowner's insurance though. The vast majority of club fields require AMA membership, partly because of the insurance and partly because of the things AMA does for the hobby. Most fields wouldn't even exist if it weren't for the work the AMA has done over the years, so clubs rightly push the membership to support them. I know a lot of guys complain about the $60 a year it costs for AMA (some even complain that you have to pay club dues to fly but land ain't free), especially after already spending so much on a plane and everything to go with it, but once you get over that initial hump you'll find that you spend more on fuel and repairs annually than you do on AMA membership.