I was a student at the time, but it seemed like GCC was like the Linux of its day, causing a lot of upheavals in the compiler market. GCC code was so fast compared to what was out there.
For the bulk of Unix user/developers, the big thing was that GCC reintroduced the idea that you should be able to get free dev tools for your Unix OS, during a time when some vendors had decided that you should pay more to get the dev tools in addition to the base OS.