Race bikes usually only have a rear brake and bikes for vert/street usually haven't got any brakes at all. Dual brakes is sensible on a bike that sees some utility use, like being ridden on roads, but removing the brake will (to some) make the bike look more "hard core", or "cooler". And, if you haven't got a rotor/gyro, removing the front brake will let you do barspins w/o the brake cable getting tangled up.
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