The issue of doing one set to failure can be viewed a few different ways. The American College of Sports Medicine considers training in this manner to be effective in terms of attaining general health. But I'm working from the perspective that you're a healthy and active bodybuilder who wants to reach their potential in terms of physical development.
Conditioning should be an important training consideration. In my mind, bodybuilding isn't just about developing bigger muscles, it's also about conditioning your body, raising it to the next level, so to speak. With that in mind, bigger muscles are just one part of the equation. Don't forget about well-conditioned muscles that can perform repetitively without tiring. And what about body composition? How can you improve your body composition to any significant degree if you perform only one set to failure? You simply won't expend enough calories to burn enough fat. So, if you do one set even to failure you'll condition yourself to only that level.
But let's take it one step further. When we talk about bodybuilding, we're really talking about our bodies undergoing positive adaptations at many levels. Changes take place at a muscle-fiber level, connective tissues become stronger, your nervous system becomes more functional, cardiovascular changes occur, energy utilization becomes more efficient, your hones grow stronger and various hormonal adaptations take place as well.
Now, presumably, you'd like to know what research has to say on the subject of one set to failure. The truth is, not much. In one study conducted by B.F. Hurley and reported in the October 1984 issue of Medicine & Science in Sports & Exercise, researchers found that although the single-set paradigm offered significant increases in strength, the measures for body composition, maximal oxygen uptake, cardiovascular performance and hemodynamics (related to blood flow) didn't change.
A recent study by J.B. Kramer, from the exercise science department at Appalachian State University in Boone, North Carolina, compared a single set to failure with multiple sets to failure on squat performance. Over the 14-week study, all subjects increased their strength; but the multiple-set group saw about 50% more strength increases than the single-set group.
Naturally, exercise scientists, athletes and coaches want to know what's the most effective way to train. Varying volume (sets and reps), intensity (amount of weight you lift) and frequency of training wins hands down. First and foremost, this means you complete more than one set for each body part, which will maximize your body's adaptations in those areas mentioned above. You'll also end up growing stronger and bigger faster. Does this mean single sets to failure have no place in your routine whatsoever? Not at all. Since varying the wav you train is key to continued progress, including single sets to failure from time to time would seem appropriate. But my advice is to do so sparingly, maybe at times when you need to cut short your time in the gym.