When do you need bridging in a floor?

Bridging is always a good idea. I did a little construction work a long time ago, and we always used thin metal strips between the joists in new construction instead of wooden bridge work. Here's a picture of metal bridging between joists. In this picture they have bridging every third of the way, or every 4' on a 12' floor. http://www.rd.com/familyhandyman/content/34459?trkid=tfhplus_november_07