Are Factory Outlet stores really cheaper? What's the catch?

I've never been to a "factory outlet" store, but friends & family tell me they're way cheaper, with no drawbacks (you still get service, the stores are still pretty, etc.) I'm not a "shopper" (when it comes to clothes & shoes), so would like to know the truth. Are "factory outlet" stores worth it? What are the advantages & disadvantages of shopping there, compared to regular stores? Thanks!