Well, then, let's put this subject to rest:
Joe's Thinking on "Reason's to Isolate"
The discussion involving full-body workouts and isolation exercises stems from a mistaken understanding of professional bodybuilders' routines. The "Muscle and Fitness" readers who wanted to be huge like their heroes would often see all of the isolation movements being done by IFBB Professionals and decide that what they were doing would obviously be the best possible answer to looking like they do.
The flaws in this particular train of thought are pretty significant. The first major issue was that most professional figure athletes have a "chemical engineering" factor that the average person who would be following their plans doesn't have. The second issue, and the one that I think needs to be pointed out more than anything else, is that they didn't get to the point that they are at by doing these exercises from the beginning. These routines are used to polish their already very well constructed physiques, and are centered around the issues that they CURRENTLY have.
To put on the most mass, multi-joint compound lifts are a superior as they allow one to train in a manner as to hit as many muscle groups as possible in the shortest amount of time. From all of the studies that I've read, the jury is still out on some of the sayings that you hear regarding drops in testosterone caused by working out for more than 1 hour at a time, squatting increasing HGH, test, and IGF-1 levels, etc. This doesn't mean a great deal, though, as a well constructed routine will be centered around efficiency and here's why from my perspective:
The serious athlete has a limited amount that they can do in addition to their main routine that will not actually distract from their recovery time. The theory of supercompensation (the post training period during which the trained function/parameter has a higher performance capacity than it did prior to the training period) leads us to believe that adding a significant amount of stress before full recovery has completed can actually cause a decrease in performance. I don't think that the supercompensation model is 100%, but it's a good way to easily explain the need for periods of the most intense training and most restorative recovery possible.
This is where isolation can play a factor. Where the are obvious weak points in an ADVANCED athlete, isolation can be used in small doses as "feeder" workouts to assist in major movements. Weak point theory serves no purpose in the novice or intermediate athlete, as they don't generally have "weak points" so much as they are just weak in general. Trying to find the weak links on a chain takes on far less significance if you're trying to pull a car, but all you have to work with is one of those little chains they attach the pens at the bank with. You need a bigger chain, and so it's best to not waste any of the precious recovery time on isolation.
Counterpoints: Isolation and smaller compounds work well for building a larger movement assuming the athlete is using a conjugate training system. They can also be used to rehab injuries if done lightly, or for prehab (which is why I do it...deadlift-related biceps injuries are very common, especially in stongman events where the pulls may not be on a standard barbell). The final point is that if an athlete is injured, they can use smaller movements to train around an injury.