Hey Greg, thats a very good question. IMO&E, total depletion at the end of a training session would be counter productive, as it would be a taking the stimulus a couple of steps too far, resulting in cell damage and the need for prolonged recovery.
The volume and intensity of the training used would of course depend upon the fiber range being targeted. It is quite easy, with experience, to feel the point where you start to near the 'bottom of the tank' in terms of muscle glycogen(MG). This is the point in a training session where I start to back off. Going home feeling tired but not completely wiped out. The term 'train low, race high' isn't suggesting training in a depleted state, it is discouraging continuously and repeatedly carboloading the cells.... this just gives the athlete more work to do in order to stimulate change. Its training with a constant tail wind!
It might be worthwhile mentioning that the MG stored in a single muscle cell is locked in that cell, exclusively for that cell's use. It cannot be accessed for use by other muscle cells or to bolster ebbing blood glucose levels. This also means that the stimulus of MG depletion is also cell specific.
I've probably missed loads out, so ask away if I have... thats a rushed answer as I'm rushing about!
Happiness is success.
Contentment is wealth.