I agree with all of the reasons previously given in favor of soap and brush. I used canned stuff for several years, tried soap and a brush on just a whim and noted a difference right away in the closeness of the shave, cost and longevity of the product.
One thing not mentioned so far that I also noticed was that the blade lasted much longer with the use of soap as opposed to the can. I would get 4 or 5 shaves per Mach II blade using the can; using the brush I would get at least two months on a Mach II. Before I went with a straight I was using a Schick Quattro IV and got 16 months out of the last blade and it was still going strong.