Roger states: "Seems to me that what the need for pit zips really means is that you are wearing too much clothing. Take some off instead."
Point taken and that works fine when the weather is warm(ish). That's not as much of an option when the weather is foul, or cold. I hike often in what we call "hypothermia weather" where it's about 40-50 degrees, rainy, and windy. Not exactly conditions you want to get wet in. I also do a lot of winter activities (hiking only being part of it) and much of the time shedding the shell isn't really an option due to either wind, precip or ambient temp.
If pit zips can allow me to continue to wear my shell, stay comfortably dry, and protect me from the elements, that sounds pretty win-win to me.
Plus, like another comment I saw above, I rarely fiddle with pit zips. Generally I can eyeball the conditions, set a gap in my pit zips, and it doesn't change for the rest of the day.