In the interest of being fair to Proghoff, I pushed through the original poster's link and found this video:
Description: A college professor takes his viewers over Zoom and on YouTube through a Proghoff intensive journal exercise.
Based on this video and my college experience as an English major, the American writing professor has been wedded to this method. If I had a dime for every time I had been pushed through a intensive journal exercise - timed writing with a journal prompt - I would be rich indeed. The method in college classrooms has been divorced from its original philosophical and psychological context, leaving students to wonder the point of the exercise.
Now that I understand what I have gone through, I must say that this method is very neurotypical in its approach, a very command-and-control system of writing production and self-discovery. More accurately, identity manufacture. It is designed to produce writing that conforms to professorial and societal norms, without encouraging individual creativity. It finds what the professors want you to find in your life, extracts it, and asks you to identify with it. It's an agenda, an agenda that doesn't understand how human identity works.
Human identities are composed of actions. Choosing to associate with particular social group is an action. For example, I am a Christian and I choose to associate with the Church, the body of believers. However, my identity as a Christian is not merely composed of my association with that group, like those with the social construction of identity would like to believe. I also attempt to follow the teachings of Jesus and live my life in accordance with Scripture. Further, I will be a Christian even if I am alone in doing so; and I am part of many social groups that I was involuntarily placed into or that I choose to join out of need that aren't part of my identity.
Recently I have been forced to confront the reality that I probably have a form of autism called pathological demand avoidance, which means I do not do well with people demanding things of me. This writing method is unlikely to be useful in my case, as it is a professor making demand after demand of me for 45 minutes: write X for Y time. My mind is not made of demands, it is made of pathways. I assemble creative works from their component parts as they arrive as ideas in my skull.
However, collegiate writing professors, in their subscriptions to Proghoff and their host of neurotypical assumptions, aren't open to other methods of writing construction and assembly. They are unwilling to allow students to guide their minds through pathways of thought into new intellectual frontiers, so they command and control student writing and thought.
But for those who can't afford a college education in writing or it is otherwise inaccessible, it may be worth giving this journaling exercise a try and seeing if it is right for you. Your writing may improve considerably.