Memberships can be used in two ways, either to:
Give members premium features on your marketplace.
This can include setting a number of posts per month, number of featured/bold or priority listings and to limit the number of messages users can send to each other.
It can also be used to lock private marketplaces to the public.
e.g. some marketplaces may require a paid membership to be part of a community. It helps to restrict the best of deals to premium users – such as early property listings. This makes sure only members get great deals.