Why do grocery stores (i.e. Ralphs, Albertsons, CVS, Vons) give special pricing for members?

Question

And what is the point of having a membership? (its just used to send you junk mail, and solicit your personal information).

Answer 1

they give special pricing so that they could get the members to come back and buy more things from their company instead of just giving it to everyone. They want their customers to be members so that they know that their customers won't get anywhere else.  Also they want to dominate their opponents.

Answer 2

If you are a member at one store and not a member at another, and you know that by being a member you will get some stuff cheaper, you might be more willing to go to the store where you are a member.  Thats why memberships start up and all the large stores offer them.

One problem with this is that if essentially every grocery store in the area offers this and you are a member of each one, neither one has an advantage.  Still, if one grocery store were to not give this option they may be at a disadvantage (at least in some customers minds) so they have to keep offering the option anyhow.