Now having jets high - I can say that it seems to be of some use. I did it and liked the results, even with a crappy brush.
High and low? I really couldn't say. I'm not experienced enough to give a practical answer. Haven't done it so I can't say for sure.
The problem is that window washing isn't an exact science. It's not possible to say, for instance that rinsing efficiency is proportional to water speed hitting the glass or some such thing. If it was, you could set up an equation and solve it for a given jet type or configuration.
Because of this, you can only really go on anecdotal evidence (like Luke's) or gut feeling.
My gut feeling is that it would use more water to little or no benefit. I've run this through the mental maths computer and the numbers really don't look encouraging.