I like using bounced light but sometimes, it illuminates the background too much, which is sometimes distracting, as in this shot:
The spill from bounced light however can be controlled however if you shorten the distance between the subject and the bounced surface. In the shot below, I bounced the light, but the background wasn't illuminated by the flash.
That's because the surface I was bouncing from was much closer to the subject than it was to the background. Specifically, the bounce surface was about 3 feet from the subject, while at the same time being 15 feet or more away from the nearest wall in the background. Consistent with the inverse square law, the subject was much brighter than the background, hence the background remained dark even while the subject was brightly lit.
Controlling the spill into the background this way allowed me to control the amount of illumination in the background. In the following shot, I brightened the background (which was lit by ambient only) by allowing the shutter to slow down to 1/30 (in the previous shot it was 1/200).
Another way of limiting spill is to bounce the light against a surface that is facing the subject while also facing away from the background, such as arches, beams (bressumers), angled walls, or furniture.
Yet another way of limiting spill is to use flags to block the light from reaching the background, but that's harder to do when shooting on the run without setup. It CAN be done however, with a little imagination, as will be addressed in a future post.
Meanwhile if you want to brush up on the inverse square law and lighting depth of field, check out David Hobby's strobist lesson on that subject.