Post workout your muscles are completely completed of glycogen, so when you take your insulin+protein&carbs, all the nutrients are shuttled into the muscle.
I'm assuming you meant to say
depleted.
Firstly, will all exercise exhaust all glycogen stores? It has already been established that the lower the exercise intensity level the less percentage of glycogen is used. When I think of total depletion I think of the mid or long distance runner that collapses before the finish line.
Secondly, this implies that muscle has an unlimited storage capacity. It is accepted that exercise reduces insulin resistance (by increasing GLUT 4 activity). Therefore an argument could be made that post workout is the least beneficial time to take exogenous insulin for stimulating lean tissue anabolism.
Hypothetically speaking, say post workout insulin becomes 20% more effective. Then you can consume 20% more to cover the energy expenditure and not need to push insulin levels higher to metabolise the added intake. Driving insulin higher than this to increase (any) anabolism requires added food (carbs) to maintain blood glucose homeostatis. So if this practice is beneficial post workout, why would it not be as beneficial for every meal? After all the body grows/repairs continuously, not just post WO. IMO the post-WO window concept receives a disproportionate amount of focus versus the rest of the day.
I realize I am going against gospel here but given that science still does not completely understand nutrient metabolism, gospel is what it really is. Arguments both pro and con will largely be speculative.
The theory that seems more plausible to me is that different people have different levels of insulin output. Endo body types have a higher level while ecto's have a lower amount. This could explain the variety of results that some get while using exo insulin - some build lots of muscle while some build lots of fat. If this is the case then ectos could find multiple doses/day (ie pre workout) effective. While mesos and endo may not find it beneficial until they build enough muscle (naturally or not) where their natural output can no longer keep up with the required nutrient intake (ie pro BBs).