I use them [Costco] for my business. I get a cash refund every year that pretty much pays for the membership. I think this year I went over by about $10 because I bought a couple of high ticket items (some air conditioners and a generator.)
I just like them. Their meat and seafood is always high quality. Their Kirkland products are great. You see the same staff there year after year. As a single person it wouldn't normally make sense for me to buy in that kind of bulk but I get stuff for my parents so I think it save enough to justify the basic membership I have.