Why invest in a full frame, 20 megapixel camera if you don't take advantage of it?
Exactly my principle (although I do not have those great cameras). Now a days memory cards are not that costly I think (at least when compared to the price of the camera into which it goes).
I try to get the best out of my equipment - so full RAW it is always. May be today I do not know that much processing but tomorrow I might learn better processing. Then if I do not have the full resolution file I shall not be able to do anything. I am not that good photographer so out of every 100 photos that I shoot I generally finally keep only 20 to 30 photos. So ultimately it is not that memory hogging exercise either. While deleting my principle is if at the computer screen the photo does not look sharp or does not please me compositionally at the first sight then it goes.