The 3 ball "hit and run" in a 3-1 count

The concept is basic. Put the runner at 1B in motion to avoid potential double plays and also to allow the runner to score on a base hit to the outfield. The batter has 3 balls on him so the reason it has a specific name is to communicate to the batter that he doesn't have to swing as is the case in normal hit and runs.

Here is the conundrum for baseball coaches. Do you risk starting the runner with a 3-1 count? It is a great count to hit in. If the batter gets a ball that he can drive there is a chance that a runner in motion might be able to score on a double or a single that takes the outfielder on an angle. Those are the benefits. But, what if that batter takes a strike and the runner gets thrown out?
Now, a 3-2 count with a man on 1st has become a 3-2 count with the bases empty.

Obviosuly, every decision has a risk/ reward ratio worth considering. I think the variables that go into play here are

1) pitchers command of many pitches
2) batters willingness to swing at something in the zone(how picky are they?)
3) runners speed

The worst scenario is a pitcher that has great command of many pitches, a slow runner and a batter with a picky eye. In this scenario, a strike is likely. Furthermore, the batter may take the pitch because it's a millimeter off the plate and a slow runner would get thrown out.

There are definite moments to start the runner 3-1, but I believe many times the risks far outweigh the rewards.