[amf12]

Well, Google values independence and so almost everyone is pretty independent. There is also consistency in the internal tools, libraries and infra used, so onboarding to the new team is just understanding their project. The 20% project that you work on is also usually a task that someone can work on independently and isn't hi-pri stuff which makes it pretty easy.

TL:DR - nobody has to hand hold anybody onboarding 20% - just answer basic questions and point to the right resource.