I used to have long hair but went skinhead/buzzed because I'm receding (and only 22, alas). Retrospectives:
Long hair carries a negative connotation when socializing with people outside of the hessian demographic, it's a first impression thing, people will treat you slightly more favorably if they think they can relate to you. A functional person won't be socially inconvenienced by his hair but for the lonely teens amongst us (presumably many forum goers were depressed shut ins at some point in their development) cutting your hair will make you much more approachable to women. Which is an infinitely more rewarding pursuit than splitting an ounce with yourself and headbanging to suffocation alone in your room.
Hair maintenance is an enormous pain in the ass. Hours of post shower drying when your hurrying to be somewhere, attempting to brush exercise induced fuck enormous knots out and scalping yourself, trailing wisps of dandruff everywhere when you change shampoo, having your 'tail make it's way into something your eating or drinking, blerghhhh massive pain in the ass.
It's entirely impractical in physical activity, gets in the way and is intolerably hot. I live in the tropics (Northern Australia) and by jove getting around with a mass of thermal insulation wrapped around the hottest part of your body when the humidity is high enough for ice cubes to float in the air is a death sentence. Oh and fighting with an Achilles heel hanging from your head is, pause for effect, disadvantageous.
For those about to cut (Antaeus' salute you), know that every time you hear a "raise your sword" song you're going to despair. The desire to head bang never abates, never leaves you. Hell sometimes I can still 'feel' my hair swishing along my back, or I'll wake up gasping in a sweat with my hairbrush inexplicably ready in my hand. Much as I hated it, it was precious to me and I loved it beyond any inconvenience. I doubt the wound of it's absence will ever fully heal, but for now my severed pony tail hangs from the stairwell light fixture. A ratlike epitaph of my glorious vertebrae destroying heritage, alas. (You don't throw away something like that, I've been thinking of putting it in a nice frame and putting it up for bid on ebay, shits n giggles y'know.)
Otherwise having long hair is about looking metal, a social fabrication. Problem is long hair identifies you as a metal head, not a hessian. Admittedly I feel pangs of inadequacy and the urge to verbalize my dedication to the cause when dealing with other long hairs, but really it's puerile dick waving bullshit (and a waste of time around here, they're all morons). It's not about being metal, it's having an image. Being 'metal' is an internal thing, naturally the external reflects the internal but it is only a reflection, a shadow.