Ralph,
At first only rarely.
My instructor said that was her experience with 4x5 and she stopped bracketing. She only used the longer exposure. I am a belt and suspenders type of person though my friends didn't believe it when I was out on Lake Erie in 30 knot winds and 8 foot waves in a 24 foot sail boat.
I felt this was useful so I increased the first exposure and then bracketed by two stops. Now I print the first exposure 30-35% of the time. Rarely I print both and compare. Usually I can tell from the negative. I meter 400 HP5 at 200 and then add bellows factor and add two stops.
When I got into 7x17, Dick Phillips, maker of both my 8x10 and 7x17, said you have to give these cameras lots of exposure. A bellow that big eats up a lot of light. Dick has never steered me wrong.
John