The real *reason* you want to have at least 2 days of battery life is dependability. I had instances where I'm too tired to place it down on a puck or slept with it on me, waking up knowing it can go through another day without being put back on the puck.
So far mine's handling 2 days like a champ (if needed) otherwise, I also charge nightly. Because gimping features on an expensive device which was made specifically to improve your interactions and communication is just not an appealing tradeoff.
I mean, it's kinda funny how Apple increased the thickness of succeeding watches for bigger batteries and LTE antennas only to go back to the Series 0's thickness.
The curse of Apple is efficiency. Once they find a way to lower power draw, they aim for the things that we wouldn't mind having (like bigger batteries). Series 3 provided the best mix of speed and battery life, even when up against S4.
Cellular support is coming soon to my country, so I'll report back if LTE idling causes a significant hit on the battery.