This question poses a variaton in men's urinating practices that I have considered before. Now that I think about it, I have observed differences regarding what guys do. For me, it is just natural to take out my entire package. I think it would feel awkward to me for the waist band of my underwear or pants to be stretched across the top/front of my balls. Subconsciously, perhaps, I also just like the feel of letting it all hang out.