I tried something the other day whilst out working on customers houses with the autobrush.
I turned the varistream almost full on so there was loads of pressure. Because the water was coming out so fast meant I had to work faster and also I didn't have to spend loads of time rinsing like I normally do with low pressure and pencil jets.
Also, If you wash the whole window frame even above the glass over spray won't effect your work.
On the other hand, if your in the habit of only washing the glass I'm sure the over spay would effect your work.