The issue of volume and intensity has probably caused more controversy than any other in the field of bodybuilding. I won't say that's true of exercise science in general because these principles have been clearly dealt with in much of the scientific literature insofar as it applies to exercise science. The one major mistake that has been made has been when transferring over the principle of 'more is better' as it applies to endurance oriented athletic training- i.e. triathlons, 10K, marathoners, and applying it to bodybuilding. This is a total misapplication of these interrelated and interdependent principles.

The issue of volume is a much-overstated one as it is actually of secondary importance when it comes to stimulating gains in muscle size and strength. Of course, you must have some volume to have a workout; no one would advocate doing zero volume to stimulate muscle gains. However, the principle of volume is secondary to that of intensity. Why is this? Because intensity is the variable most reputable exercise physiologists have cited for over 100 years as the major stimulus that causes strength/size gains.
The issue of sets and volume is a critical factor in the definition of HIT training and the one most likely to miss-stated and/or misinterpreted. Arthur Jones, the true originator of HIT- at least in a coherent form, originally started off perfuming 4 sets of each exercise. He did this in his workouts for a number of years never surpassing about 175 lbs. After giving the matter further thought, he cut his number of sets in half, without making any other changes, besides this reduction in volume. Within a few weeks or so, he had added 12 lbs.
This means a 50% reduction in the number of sets performed gave him a significant increase in muscle mass!
Note: Many bodybuilders, even those on steroids, would be quite happy with a 12 lb gain in muscle mass in such a short. Indeed for most, that is more than can realistically gained in a year- at least on continual basis.

Probably the most extreme example of HIT type training- at least in respect to low volume- is Mentzer Heavy Duty training, particularly the versions of it that were recommended circa 1994- 2001. The two or three sets every 4- 10 days or so, currently cited by many uninformed individuals as the end all and be all of HIT, was a very extreme method that Mentzer developed in Heavy Duty 2 known as the consolidation routine, as a response to the problem of impasses in his client's progress, which he attributed to overtraining, which may or may not have been true. What is important to remember is that he was working with individuals with genetically average and even sub average recovery ability (those individuals who had FAILED with other methods). It is quite possible that these individuals may indeed have not been progressing due to insufficient recovery methods. The training that Mentzer has his clients on prior to the mid 90's- (I have first hand knowledge, I was one of them)- was originally two days on, one off, two on, two off, with all sets done to total failure with forced reps and negatives at the end of each set. This proved to be too much for most, if not all his clients- including myself and thus then he scaled it back to the routine outlined in Heavy-Duty 1, a 3 days a week program separating the body into chest/back, delts/arms and legs, which worked great for many. I personally have made my best gains training on average 3 times a week- sometimes 2- sometimes 4- but as I've become stronger, 4 days a week is too exhausting, and doesn’t allow enough time for recovery to take place. Even training 3 days a week can be too much for some individuals. The principal of individual differences states that trainees aren't identical, though we all possess the same underlying physiology and anatomy, and MUST be taken into account when designing or implementing a workout program for a client or for yourself.