I do not think that's the point. Let's say you had a build that took 7 hours but if you took all the steps the author did, you would be able to build it in 30

I do not think that's the point. Let's say you had a build that took 7 hours but if you took all the steps the author did, you would be able to build it in 30 minutes locally for debugging. Would that be interesting? That's about the amount of relative improvement the author saw. Size of input varies, finding solutions to unnecessarily long compiles in rust are useful across many of them.