I'm well aware of the joys of optimization, I just haven't come across someone building multi-GB executables at a pace where milliseconds spent linking mattered.

To me that's an exotic workload which sounds interesting, hence why I'm curious.

Well, keep in mind that the full linking step has to be done at the end of an incremental build. So if you're a developer actively working on a project with a 4GB executable, that linking time is part of your edit-compile-test cycle, and you have to wait for it every time you change a line of code.

The benchmarks on mold's README show that GNU gold takes 33 seconds to link clang, whereas mold takes 1.3 seconds. If you're a developer working on Clang, that's a pretty serious productivity improvement.