I have only been an actual assistant coach for about a month but I like to imagine that I've been helping mentor my teammates, especially the younger ones, for years. The advantage is that I am so young that I can easily relate to their situation. The disadvantage is that I don't know everything. Also, I am a runner with the other 41 million Americans that run so I can not comment on "common" team sports.
In running a large part of the performance of a race is based on physical limitations. From the 2:13 marathoner to the 25:30 5ker everyone is gasping and has burning legs at the end of the race. For a coach the pressure is on to maximize the performance of the athletes at some race or races. I was reading Brad Hudson's book "From the 5k to the Marathon: How to be your own best Coach" and he gave the following example. In sailing you can take multiple courses to get to your destination. He said you could sail into the wind at a steep angle and go slow or take a more shallow angle and go much faster but have to tack back and forth. I created the chart below as an example:
The point of this is that you can not push your body to the limit every day and hope that it will achieve the results you want as quickly as if you varied the stress on your body. That means taking it easy sometimes and listening to your body. It also means that it is okay to add on more mileage or repeats or run faster if the athlete is feeling good. Why slow down an athlete's progress?
Malcolm Gladwell in his book Outliers suggests that 10,000 hours of practice is what is needed to move someone from the bottom of the pile to the top. This goes along with what my friends and I discovered by experience: To get better at running you have to run more. So there you have it. The shortest description of how to maximize physical potential that you will probably ever read.