I got my start professionally photographing portraits and models outdoors. As a poor college student, I didn't have the funds for flashes, umbrellas, and the other paraphernalia that indoor portraits require. Fortunately my alma-mater, Michigan State, had extensive park and garden areas available that made ideal locations.
I still enjoy working outdoors. Lighting is much more natural, and being out of a studio environment tends to relax subjects more. I try to avoid an overly elaborate setup, preferring a flash with diffuser attached to the camera with a rotating flash bracket. Put the sun at the subject's back, add enough flash to fill in the facial shadows, and everything's ready to go.
Last week I was contacted by a member of my synagogue, asking if I could shoot a portrait for use with her daughter's upcoming Bat Mitzvah announcement. It needed to be done quickly, and the fact that I would come to their house to shoot the photos was a big plus. We had the option of shooting inside (I had my flashes and umbrellas in the car), but we had a nice day and they had a nice front yard, so everyone agreed that outdoors was preferred. The rest of the family sat on their front stoop while we shot. I used the dark hedges for a background, making the hair highlights really jump and helping to separate the subject from the background.