No first hand experience here, but I’d have to agree with Ryan, the early stages of the project are the foundation for the future stages. Im sure small aspects can overlap or melt between two process groups, but it would be pretty impossible to move on to the next stage if the proper documents weren’t able to be completed and approved. When your closing out a project you will be looking back and making sure all the details are correct and complete and if they aren’t then you will have to go back and fix/finish, and if you do encounter a problem then depending on its severity or the changes that would need to happen in order to fix the problem you could end up derailing the whole project. The monitoring and controlling process group that happens all throughout the project is the main line of defense against this type of scenario.