The phrase "difference someone have made" means the impact or change that a person has brought about. It refers to the positive effects or contributions someone has made in a situation or to other people's lives. Full definition
It's difficult to evaluate the level of risk, not knowing what difference it would make in the same kind of circumstances if he had been or gets neutered. (samthedogtrainer.com)
Just imagine what a wonderful difference this has made for rural and remote people and communities! (croakey.org)
You'd be shocked by how much difference you'd make in your home with few decor pieces and furniture. (asakemi.com)