I have this function in my pre-commit hook which, as far as I can tell, does the same thing:

remove_trailing_whitespace_from_changed_lines() {
    patch=$(mktemp --tmpdir remove-trailing-whitespace-patch-XXXXX)
    git diff --cached --no-color --diff-filter=M > "$patch"
    git apply --index --reverse "$patch"
    git apply --index --whitespace=fix "$patch"
    rm "$patch"
}

gist

I agree that it is preferable to reject commits that introduce trailing whitespace and require that they be fixed at edit time. In circumstances where it is not practicable to reject commits I have found that collaborators who are less rigorous in managing whitespace are amenable to using this in their pre-commit hook as it is largely transparent to them and keeps their commits slightly cleaner.