But KevinF, what about the Flappy, Flappy noise, oh make it stop that annoying flutter like some kid flying a kite against your head sound!!
OK, I over did it there but tighter bike clothing is not just about the drag but about the annoying noise that gets between you enjoying nature and hearing the idiot cursing you out for riding on the street!! :O
If the flapping sound is loud enough or distracting, that can take away some degree, although small, of enjoyment and maybe even safety. Your ears are important in riding too. I also had that Canari jacket billow up and block my vision through my mirror.
One other benefit no one brought up is sweat management. Tighter clothing is more apt to absorb sweat better keeping you cooler and drier. Tighter clothes might also chafe less either from the lack of movement or from the better sweat management.
Finally, I like the stuff because I feel more athletic, look a little leaner (almost a glimpse of what the future may bring if I shed a few more pounds) and I tend to push a little harder because of it.
In the end, wear what you like.
Frank