In the early years of my training, I kept great records in journals. My notes included nutrition, cardio, supplements and of course every weight training detail. What I learned was that each muscle group had a decent range of energy substrates they could store, which was dependent on my current nutrient intake and training schedule.
A key learning is that when glycogen levels are fit to full, I could perform around 16-sets per muscle group before my pump faded. This meant the stored energy in muscles trained had gone to very low levels, and that the necessary waste products had congested the crime scene so that getting more of a pump was impossible. This is time to move on to another muscle group or simply exit the front door. I also noticed if my carb intake was reduced that about 12-sets brought me to a max pump, and I headed out.
Nothing scientific but it's easy to see that when energy substrates fall off, so will performance and your ability to get just a bit tighter pump. Now you know when to move on, or move out in the gym.