During a 5k race (about 3.1 miles) I do not take any sort of break (fun money). I can make it to the end without taking water, food and without walking. If we were a few weeks or months from our sailing goal I'm sure we would not have a fun budget. We would not need a break as we would be so excited to save every penny.
During a marathon (about 26.2 miles) I need a break. I need water and maybe a walking break and some food. Without water I would be unlikely to finish a warm summer marathon and would finish much later in any weather. In the same way, our fun budget recharges us, keeps us going, and might get us to goal faster. We would likely go nuts without a fun budget for the next 5-7 years, just as I would likely "hit the wall" faster without food and water during a marathon.
We don't want to go nuts. We want to go sailing without debt.