I can guarantee you that I have jumped over to my browser when doing a compile that is definitely limited by my machine. I'm ok doing this knowing that I will only take up so much work on my machine. I do not go off and kick off another giant compile at the same time.
Now, if the browser becomes more and more consuming, hitting my browser could get closer and closer to kicking off another giant compile.
I could almost guarantee you this is not the bottleneck of any modern setup.