Think of it like computer.
Every open task that you do not finish is like an open tab on your browser that is draining your battery, taking up memory and a constant distraction. Over time, it will take a toll on your body and mind and then things start running slower and kill your battery.
The your mind doesn't want to look at it any more and it is just there. You say you are going to close that tab but you never do, instead you open another and then another one.
With this system, you learn to close those tabs with no thought. You conserve your minds browser and complete each tab. You system now runs on the same system, just faster and less congestion.