Upload & Sell: Off
MRAW and SRAW are the result of either pixel binning or pixel combining (im not sure what) its not Cropping as you still get the full 1.6 crop image.
of the 2 methods if its binning then unless you just want the smaller files Im not sure I really see the point. Hard drives are cheap and you can save at any res you want after but can add ress from an Sraw.
If is combining then you potentially have a noise benifit beyond just looking at a smaller image thus not magnifing the noise as much , which you could obviously do by reducing the res in post.
All that said the 18mp cams Mraw is around 10mp which is a res which my 40D has and looks very good at (and I still have room to crop)
1 Note of caution though is that not all Raw progs play well (if at all) with M and S raw