That license, and others derived from it, are at the root of most non-proprietary software and many types of user-created content. Using the internet means you've used software that likely could not have been created without such licenses. Wikipedia is another example of something using a license derived from the one he helped create.
Helping create flourishing communities of people legally sharing each others' work, collectively creating great works, influences legislation. Imagine if no licenses existed for people to legally remix each other's work without explicit permission. Disney, the MPAA, the RIAA, and others would have had greater ability to lengthen copyright terms, increase penalties for infringement, and so on.
Microsoft had a strong play for extending from the desktop to servers when Unix was fragmented. I wonder what might have happened if apache didn't exist to compete with Microsoft -- how much more influence Microsoft might have had over U.S. legislation.
He's done a lot more than just help write the GPL, but that alone contributed a lot.