Yes, I developed the habit from shooting 4x5 transparencies. I generally do it on neg film too, if I am using a tripod and such. I figure I may as well, since I have the proper filters in my case anyhow. I want to apply the CC to the sky and everything else in the picture equally. The same CC that will make the ground look pretty much how it looks will also make the sky look pretty much like it looks. The problem is thinking that a sky will turn out neutral, when you can look right at it in person and see that it is not really neutral at all.
+2,000 K over clear noon light is indeed a large jump for mid day...but time of day does matter as well, as does the vastly variable definition of "overcast". I view it as everything from thin clouds, to fog, to storms-a-comin'...anything in which the light is coming entirely through the clouds instead of directly from the sun.