Well, here's the situation. You're on an outdoor trip in winter. It's cold outside and after a long day all you want to do is crawl into your warm sleeping bag and not get out of it until the next morning. Unfortunately, shortly after reaching the warmth of your tent, you feel the urge to pee and have to get up and out again.
The obvious solution to just pee right before you go to bed doesn't seem to help as somehow the act of warming up in the sleeping bag seems to encourage a second round of peeing.
It's ok in summer, but in winter it REALLY sucks, especially if you're traveling light so you only have your ski boots to get into and your tent is small and cramped anyway...