If you intend to stay only on larger commercially run sites and have insured your caravan elsewhere then club membership may not be for you.
As already mentioned though, the certified networks of sites run be either club provide opportunities to visit quieter rural sites away from large towns, bars, swimming pools and amusement arcades, rallies provide inexpensive opportunities to use your caravan to it's maximum potential, sometimes in places that you wouldn't normally be allowed to stay on and either of the club insurance organisations set the standard for others to follow.
Some years ago we bought our first ever factory fresh brand new caravan which we insured 'new for old' with the C&CC.
Three months after we took delivery our caravan was written off in flooding but our C&CC insurance took the stress and worry from this bad situation with their highly professional prompt no quibble approach. We continue to insure with them and have no hesitation in recommending Club Care insurance and we continue to be members of the C&CC.
I should imagine that the Caravan Club have similar high standards so which one to join is a matter of personal preference.