Sometimes you copy files into your GitHub repository on top of existing files (for example, syncing some code from an external source).
This can cause the file mod / chmod to differ, for example some files are
0644 in the repo and
0755 from the folder you copy. Git picks up on this which can cause a lot of confusing diffs to sift through.
With this one-liner you can remove all the chmod file changes before making a commit:
git diff -p -R --no-ext-diff --no-color \ | grep -E "^(diff|(old|new) mode)" --color=never \ | git apply