you dont HAVE to replace the high beams if you do the lows. but that is your choice...
most people do not put HID into their high beams solely for the startup time for HIDs
its not good for HIDs to be turned on and off constantly and flashing to pass with high beam HID can burn a ballast out real quick, unless its bixenon in which the bulb just moves in and out for focal purposes which you could do endlessly.
I only have low beam HID in my silverado, but if you lets say do ALOT of off road driving or use your high beams very frequently then why not hook them up too.
Summary:
if you use your highs alot go for it
if not, dont waste your money, but like i said your choice.
good luck
