I read a lot about that kind of thing when I was researching the oil catch can. I saw that people were saying that the piston rings don't seal correctly when you don't have that breather hooked up. It also does not allow for correct vacuum pressure within the engine (from my reading). I guess it all comes down to why? If you can get a little hose that was originally part of the OEM design, why wouldn't you? Some engineer in Japan decided that it was a good idea to add that hose, why should we argue with him? h: