I worked in BigCo on a big (and commercialy successful) software project used in hospitals. More than 1,000 people (soft devs, QM, sales&marketing) are employed by BigCo to work on it. Even when I contributed less than 1/1000 to the project, I believe my contribution to the world is still quite big, since the software is deployed to 10,000's of hospitals and assist with (sometimes life-saving) procedures every day.
I think with anything, you can somehow relate it to making an impact in the world. I could say working at a consulting company who's on a project for a car manufacturer, on a project that improves the data quality of owners of cars - i'm making an impact because with better data, people are getting the right information / advertisments for cars that are right for them, thus improving their lives by helping them choose the right car. Obviously, this employee is many layers away, but he could still say that he is still making an impact in some super small way.
I think it really is just up to the individual to see what they believe is enough of an impact for them personally.