Rear Disc brake conversion question

when i put ls1 camaro brakes on all 4 corners, i modified the prop valve per instructions from baer brake rear disc kit. works really well hth.
 
What is the Down side to not doing the Prop valve Mitifications and just leaving the stock one in place??
 
rear brakes can lock up before and harder then the front and cause the rear to come around on you in hard braking.
 
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