Fast compilation times are a human-centric goal. The machine couldn't care less if it takes a millennia to compile your program. Only humans care about fast compile times.

But, I'm not sure that is even the primary benefit. The primary benefit is that you won't be incentivized to leave unused imports and variables to litter your code, as I see happen all the time in languages that aren't so strict. The Go team has even stated that they decided there would be no warnings because they've learned that warnings get ignored.

I think it goes both ways. Yes, eliminating unused variables and imports accelerates compilation. Also, compilation speed is a great deal for Go, but keeping the code devoid of unused variables also reduces the cognitive load of humans a lot. Keeping language simple is another feature which helps both ways.