I do training with minimal rest a lot (whether it's supersets or HIT or whatever you want to call it). I only take 45-60sec breaks between sets and maybe 60-120sec break between exercises/circuits. I tend to finish in a very short period of time. Ex: today I did 4 sets of flat bench, 3 sets of decline, 3 sets of barbell rows, 4 sets of seated rows, 3 sets of cable crunches, and 3 sets of obliques in about 25 minutes. Obviously with more rest the time would be longer, but I wouldn't be doing any more sets. So does it matter than I'm done in 25 minutes instead of 40 or 45 (or whatever it would be)?