The IMAA card in addition to HF magazine that features giants scale articles, advertising and IMAA event coverage allows you to fly in IMAA sanctioned events. IMAA is SIG, like SAM, IMAC, JPO, NASA, NFFS, VRCS - most if not all of these special interest groups under the AMA have a magazine or newsletter for those that are members.
Is membership to theses organizations required - no, is it desireable - those that are members apparantly think it is.

Red S.AMA 951
IMAA 18939, LSF 412, VRCS 951