Maybe it's just me, but if my feet are in boots they tend to become hotter than if I were to wear tennis shoes or sandals. I sweat 2x as much when I wear boots as when i wear sandals, and close to that when I wear tennis shoes. I take off my boots when I enter my house after work, and within 20 minutes I feel what has to be 5 degrees cooler. This isn't really an issue today, but we're talking about a scenario in which you may not have the luxury of a readily available (and safe) water source that you can depend on for re-hydration, making the amount your feet sweat and your total body temperature (and therefore how much the rest of your body sweats) something to monitor closely.