> It is sometimes just much nicer to bind stuff together directly. Yes. It's so much nicer to have your hammer at your desk than to go to a cabinet to fetch it when you need it. But if you own bunch of tools and do various task at your desk it's either cabinet or a pile on you desk that at some point prevents you from making any progress on your projects.

Things should be kept separated out and organised by concern. If they are brought together it is either for convenience or speed. Both perfectly valid reasons so the separation is never strict but should be viewed as exception not as a rule. If you don't watch yourself you might end up with oscommerce PHP source files where everything is together because it's so much nicer to bind stuff directly.