Most professional players finish their swings with one hand on the bat. Younger players imitating this swing can run into problems by letting go of the handle too early, resulting in a very poor swing. They need to understand that the bat is pulled out of the top hand after contact with the ball because of the emphasis on forward extension. The hands extend forward to the point where the top hand can no longer hold onto the bat.

If this type of style is adopted, the top hand should end up touching the front shoulder during the follow through and the bottom hand should finish a little above shoulder height and away from the body (unlike the two-handed follow through where the hands are both above the front shoulder and close).

A word of caution

The one-handed follow through places greater stress on the front shoulder. This can especially be a problem for younger players who bat left and throw right (or vice-versa), increasing the strain on the throwing shoulder when hitting. My youngest son bats left-handed and is a right handed pitcher. He hurt his shoulder in soft toss with the one-handed follow through and subsequently hurt his arm further when pitching. He was 11 years old at the time. We abandoned the one-handed follow through (and sent him to therapy) and he hasn't had a problem since. The point is that a one-handed follow through should probably be avoided until a player is 13 or 14, especially if they throw opposite of the way they bat.