>>2944374for milkyway stacking its mostly for noise reduction.
for deep sky objects like galaxies and stuff its to bring out the details and sharpness and also to reduce noise.
You can stack pictures without darks bias or offset frames but the results are not going to be as good.
I usually tend to take a few darks maybe half of the lights i have.
Heres another try on m33 using deep sky stacker to stack the images. ~25 lights and 14 darks. DSS is good for stacking but it refuses to work with my raw files, it reads them but registers hundreds of thousands stars or none. I have to convert my files to a bit smaller jpegs for it to work properly.