To be able to apply makeup, fix their hair, maybe talk in quiet on the phone for a second, and of course pee, in a place where there's almost no risk of some drunk redneck deciding to beat the **** out of them.
They're never, ever, ever just there, like, creepily lurking. They completely blend in because they're just doing the normal bathroom things for a normal amount of time.
I've always felt like they made the women's bathrooms safer, and I bet if I were to take a poll on facebook of women my age in my city, other women would overwhelmingly agree, but Memphis is, like I said, Big Gay Historically Drag Friendly Central, and I hang with a very "social justicey" crowd, so the poll would be biased.
People who are not comfortable with them just don't go into the city limits proper anyway, and avoid "the real core city" like the plague, because it's filled people of all kinds of freaky-to-many subcultures, as well as often being the city with the highest homicide rate in the country (and we're a rather violent country!) because of poverty-related gangs and drugs.