Glad I am not the only one that doesn't get mitts. I was half expecting to be mocked and trolled for not seeing the point.
Windshirts on the other hand, I get. I don't always bring one, but I often do, especially on section hikes and summer trips. For me it is about fine tuning warmth, and for around 100-200g depending on what kind of windshirt, it is not that much of a weight penalty. I have one that is 75g that sees the most use, but I also have a beefier running jacket that is around 200g that I use in cooler temps because it is warmer (plus has nice pockets too as a bonus). I have yet another that is 140g that is in my urban backpack that I use a lot as an extra layer--great for when I stay out later than expected and it's much colder around midnight.
Even in places that see a lot of rain, which probably includes where I live and hike, it is usually not raining. So my windshirts see more use than my rain gear. Plus it is multi-use: you can wear them to bed (I often do), wear as a shirt while you wash/dry your t-shirt, and if it is warmer out but raining it is a nice buffer between a rain jacket/poncho and arms (if, like me, you don't find rain shells as nice on the skin as windshirt nylon).
Now the whole pee bottle or pee in your pot thing I don't get either. Not because I think it is "gross" either--fresh pee is sterile, from what I gather. I just don't mind getting up to pee outside of my shelter, even in the rain. Only takes a minute or so, even when squirming out of a bivy. Maybe because this is not as frequent for me? I hardly ever wake up at home to pee, and would estimate that I wake up to pee out backpacking maybe 20-25% of the time. I do make it a point to try and pee before bed, though.