Photography is all about location and when shooting portraits is concerned, it is an important factor to consider. If you decide on shooting in an indoor studio set up, you will have complete control over lighting as your subject stands against a plain white background. However this plain white background becomes dull and boring and you will most likely be sitting on a stool or standing whereas in an on location photo shoot, one can take advantage of what is available such as tree, park bench, beside the lake etc.
A shooting is a series of frames, that runs for an uninterrupted period of time. For portraits, I always prefer to use natural light because natural light is something that is freely available to all photographers. Paying more attention to constantly changing levels of natural light is the most important step to improve your photography as one must react quickly based on the amount of light available at the given time in order to produce a good photo.