I spent some time about 4 years ago going through the PSP book. The first thing to note is that the initial research on PSP was done on a very small sample size

I spent some time about 4 years ago going through the PSP book. The first thing to note is that the initial research on PSP was done on a very small sample size - grad classes and some small groups of professionals. So you have to question the efficacy of the original research. The process itself largely consists of piles of paperwork. Piles. Tons of overhead monitoring your work. All that said, the intended goal was to create a state of mindfulness of your software creation process, allowing you to understand the typical root causes of bugs and better estimating.