You will see your neighbors awesome display/frag tanks and meet with other aquarium enthusiast that enjoy the same interesting hobby. It may not be obvious to the casual observer, but reef systems are anything but simple. Synergy of the group discusses may help solve problems/issues that an individual alone may have difficulty solving. There is sharing of experience and knowledge on issues with corals, fish, equipment, etc. This is a very interesting and diversity group. The level of participation in the hobby is up to you.
Thanks,
Gary