I belong to two locally, plus our state guild. For me its seeing what everyone else is doing, and getting help when I have something that's not working. Plus the programs and classes offered by the guilds is a great place to learn new things. Am signed up for a dying class in January. Should prove interesting.
The guild also has a library so quilting books are always available to check out.
One guild also has a "workday" which is come and bring your own project OR there will be a class of some kind. Usually taught by a member and only costs $5. People take turns bring in some new technique or some cool design to work on.