I'm sure that most people who take up caravanning do so because it seems to offer a degree of freedom to visit places, on their own terms and generally at a lower nightly cost that having to use hotels or bed and breakfast accommodation. This is particularly true if you have a family.
Owning and using a touring caravan only makes sense if you are going to make good use of it, in other words not just a two weeks a year, Otherwise the cost of ownership will be likely to exceed the cost of a family package holiday. So caravanning is more likely to be for those who want to be able to make a lot of use of the caravan.
This is where the Clubs can start to make a difference. Firstly they open up the range of sites that are available across the country. Some sites are not available to non members. The clubs also provide some guarantees of the standards of the sites, and a complaints procedure if there are failures in that respect.
Club membership can sometimes include discounts at some sites.
The clubs offer car and caravan insurance and breakdown packages, that are properly tailored to the needs of caravanners. They may not be the cheapest, but you be unlikely to find better overall packages - check the small print especially about recovery of caravan sizes.
Membership also gives access to a range of other services such technical and legal advice
There are sometimes club member meets, some are quite large and caravan suppliers have trade stands where you can pick up items at discounted prices. You can dip into there additional facilities as and when you want.
So you can make as much or as little of club membership. As for teh difference between the two clubs, Some will say one is better than the other, but that depends on your personal preferences.