I have been instructing gliders for about 27 years, and for me the boying the wake excercise is essential during pre-solo training.
Part of it is to show the student the limits of possible positioning behind the tug (and on the lateral positions of the box, the tug pilot will have to use quite some rudder to keep going straight), and especially to show the point beyond which immediate release is mandatory on high positions.
Low position (well below the wake) is something the student needs to learn for descent and approach on tow anyways.

Having said that, there is no aggressive maneuvring involved at all, with me talking the students through the excercise. Changing positions is done gradually all the way through the excercise, with constant tension on the rope.

It usually is an excercise which is flown once with the student, and at some point when he is at a level where I don't have to interfere anymore on a normal tow.

Bert TW