Controlling light is important outside as well as inside. But, it's not easy to find a lighting instrument that can compete with the sun! Larger HMI's can do the job but they're expensive.
Most outdoors lighting is done using the sun itself as the light source. You use bounce cards, reflectors, and mirrors to direct the sun where you want it to go. You can also employ nets & scrims to cut down the amount of sunlight, and silks to turn the sun into a large softlight. A "butterfly" is a large frame that you use to mount these fabrics in, usually 6' x 6' up to 20' x 20'.
Shooting outside is a pain. Wind, changing sky conditions, rain, ambient noise, airplanes, helicopters, sirens...
Some good advice from Barry and John. The absolute best time of the day to shoot is withing 45 minutes of sunrise or sunset--the sweet light. However this presents some logistical problems especially if you have a lot to shoot. At least avoid 10-3 like the plague--it does complicate things.