[bethling]

It's still really important. There's a cost to training and getting an engineer to understand the problems and scale that Google faces (some might come in with that, but many do not). There's also domain/google specific knowledge that's expensive to replace as well.

Yes, if someone leaves after 4 years, it's possible to hire someone else of the same ability level, but you're going to spend time and effort to make them as effective as the person who just left.