At one instance, I was discussing a product deadline with a startup. Their deadline was 4 months into the future, and my objection was that would probably not be the wisest thing to do. Startups are about learning per dollar spent, and if you’re not able to ship (learn) often enough chances are you’ll fail.
Whatever you’re going to do will take 4 months if you give it four months to complete. It could be that the activity actually takes 4 months to complete regardless of how you divide it up, but it’s an unnecessary risk to take. Plan for shorter periods, which is the essence of Scrum, is a good idea. And Parkinson’s law is part of the explanation why it’s so popular.
Parkinson’s law can also partly explain why large organizations tend to grow fat and lazy. When you have limited resources, you can’t afford to hire for “somewhat necessary” roles. If it’s not super urgent and important, you’re not doing it. As an organization grow, you will have less control of how extensive any job is. If a job needs to be done, you can afford to hire someone to do the job, and so you do it. The risk you run over time is if the “job to be done” could be done in less time. Parkinson’s law states that that won’t happen, rather the person(s) involved will overcomplicate the job so that it fills the time available. This can be super contagious over time, and kill productivity, morale and so one - and can help explain why large organizations are slow.
I love this mental model/universal law, and will continue to look for places to use it going forward.