You only need AMA if you fly competition or an organized field. I didn't know about AMA until my first contest.
No, you don't NEED it, but isn't the idea of having great insurance a good reason to have it?
Liability Coverage for the Operation of Model Aircraft, Boats, Cars, and Rockets:$2,500,000 Comprehensive General Liability Protection for model activities for members, clubs, site owners, and sponsors
$25,000 Accident/Medical Coverage for members
$10,000 Maximum Accidental Death Coverage for members
$1,000 Fire, Theft, and Vandalism Coverage for members
Primary Site Owner Insurance ‑ up to $5,000,000 each location[/i]