Shooting at reduced resolution

Not sure if this has been asked before, for RAW captures with dimensions less than its native resolution, is there some sort of pixel-binning or combining to downsize to its selected output?

Eg the 6D has a 20MP native, shooting at medium-sized RAW outputs 11MP, at small-sized RAW outputs 5MP. When shooting at 5MP RAW will any pixel-combining be done? Any advantages (like lesser noise, better DR as 4 pixels combining to 1 pixel) or disadvantages?

for a highly technical, head-exploding explanation you can look at this doc:

http://dougkerr.net/Pu​mpkin/articles/sRaw.pd​f