If your fingers are "stiff", then many women will be happier ....
No, really, if they are stiff, as they can get when we get older or when arthritis strikes, it's the pitch that usually needs to be adjusted. I do not believe inserts affect this. You can use them or not as your preference dictates. My friend has as much as 3/4" reverse in one finger and he is younger than I am. I still use 0 reverse when I can bowl.
Your span and pitches should always reflect your hand's physical make-up: bones, tendons, ligaments, skin.