I've been watching the progress of a house build that a co-worker is
going through via pictures that he is taking.

I've been able to explain to him just about everything that the
builder is doing except for this:

On both sides of most large exterior openings (large windows, patio
door, etc) there is a short, horizontal length of a 2 x 4 spanning the
interior side of 2 studs with a bolt through the sheathing and 2 x 4,
secured with a lever nut (similar to the link below) on the 2 x 4
side.

http://www.mini-lathe.com/Mini_lathe..._nut_lever.jpg

These braces appear to be holding the sheathing against the exterior
of the studs. Were these braces installed prior to nailing and have
simply just not yet been removed or do they serve some other purpose -
like wind load protection or something like that until the house is
closed up?

Thanks!