You get

the availabilty of discounted Ferry prices
Special European travel insurance ( Red Pennant -- the best product for European touring available )

As well as
Caravan Club sites which are high standard facilities but no commercial frills

Certified locations -- 5 van sites that could be anywhere and cost from around £3 an night to £10 a night they could be totally basic (water and drain only) to having stuff such as a swimming pool for site use only

plus there are all kinds of other stuff
monthly mag
regional groups that organise rallies
caravan insurance
and more

there is another group that does similar ( Camping and Caravanning Club) but I am a CC member and have been all the time we have had our caravans

we are no longer regular campers, we started off with the Caravan club but left after 2 yrs and joined the camping and caravaning club, Both offer excellent membership packages, have their own first class sites and offer other benefit's, but as we had an old caravan we felt the members of the CC that we met treated us as lepers and didn't like us parking close to their newer vans, the C&CC on the otherhand we found the members more friendly and always willing to give help and advice,

you pay your money and take your choice either way i would recommend you join either of them

Brian