If the salvage is the same color and not noticeable I do not bother to cut It off. However, if it is white or definitely not the same as the quilt fabric, it could possibly show at some time and then I am sure to clip it. However, I never have had a problem with unusual shrinkage. Seems to me like this is one of those things that we do because it was always done that way. That happens to me a lot.
I find that especially true when I decide to take a class and find out how to do something completely different than the method I had always used. Funny how the new way works much better and Is faster.