its partially based on fit, the way i understand it. depending on your style of handlebars and your seatpost height, there may be an ideal height for the fork. this, of course, can be adjusted further with the use of a stem that inclines or declines. i was told that it might not be good to cut it down to the absolute minimum (no spacers) mainly because you can't ever add height back onto the steerer, and it could affect the resale value a little if it's less customizable.