Rich,
I have heard of people not using flats or bias frames but there are only very limited circumstances where you would not use a master dark frame. The only time I do not use a master dark is when calibrating my flat subs before integrating them. The reason is that my flats are usually in the 5 second or less range (I use sky flats) and at such short iterations there is not much difference between the bias and dark masters and I can avoid shooting an extra set of short darks. But for lights of any length (and I include anything 30 seconds or longer; though mine are typically 10 minutes for RGBs and 15 minutes for NB) you need a master dark to properly clean up your images. You can reduce the amount of noise that the master dark contributes, if that is a concern, by shooting lots of dark subs, but even 25 darks will build a nice clean master dark (though because they are so easy to shoot, I typically use 50 subs for my master darks and 100 subs for my master bias; note that for flats, however, I only use 5 subs to build my master flats).
Shooting flats is easy and they really help clean up your images so you should always use them unless you have a really good technical reason for not doing so.
Hope that helps,
Jim
