When I first began posting on TNBW, I was making changes as I received feedback. I found I wasn't moving forward very fast. I spoke to several authors on TNBW and they said to complete the first draft before spending time on revisions. I will occasionally correct typos, but that's it.
Once I followed their advice I was able to complete the first draft and begin editing. A more efficient process, at least for me. Otherwise, I'd still be working on The Kurdish Connection instead of it being under contract. I've also found not everyone catches the same nits. Case in point. I had a typo in a sentence regarding a plane (but I had plan). Only two readers out of seven caught it.
Why do revised chapters require another review? Because there are very few perfect people. Editors always re-read after sending a manuscript back to an author for changes. The posting process on TNBW provides for different versions, which allows those re-reading to earn additional points.
If anyone thinks their time is wasted reading my work because someone else in the group has already reviewed a given chapter, feel free to skip to one that hasn't been reviewed. Everything helps in the end.