And from the first quote, which I strongly agree with, it follows that when people leave the company after building something together, the organization is losing something invaluable. I am baffled that this is not understood and I have witnessed first hand how great teams that are able to work well together collapse and the company has to rebuild the knowledge, wasting time and money.
I suspect most of the time that's because you can't justify keeping a team idle for even a week between projects if that's what it takes to ready the next project for them to work on. I'd be surprised if most businesses even allowed a day of idleness to get a running start with a well-functioning team.
I had a friend who worked as a project manager for a major telecom and their policy was to basically furlough her for a few weeks (paid time off) after a major project winds down. She's there if something bad happens, but otherwise it's downtime (and retained experience!) before the next project. It seems like a sensible and healthy policy.
Which is why the concept of 20% time is important. It means that 1 day a week your manager can't tell you what to do, so you can work on whatever you think is most important. You could use that time to work on what your manager wants, and most do, but if you have things that you feel are more important you just go and do them.