When a window is installed, where should it be shimmed? My window instructions say 4-6" away from corners, and at every style and mullion point, then every 15" in between, all around.

The windows were installed yesterday and, there were a few shims on the corners and bottom stiles, but that was it. Should I ask the installed to put more shims as the manufacturer requires? I watched them install a few of the windows, and they used a level to make sure it was plumb and level, and they measured diagonals so it was square. But my understanding was that the shims help to hold the window in place, and not just the nails around the fins.

Any help will be appreciated. Thanks.

If you have trouble with the windows, the first thing the window manufacturer will ask:   were the windows installed according to their instructions.  I have noticed a lot of framers (Southeast) will not bother to install shims especially if the window has mounting (nailing) flanges.  Sometimes, the windows will sag or shift which will cause the window to be difficult to open or close.  In my opinion, the proper usuage of shims can prevent this from happening.