Only the driver's side of the front diff is secured to the cross member, to control the clock-wise torquing of the diff while moving forward. However, when you get on it hard while in reverse, especially with larger tires or tires with lots of tread bite, the diff assembly wants to torque counter-clockwise which can crack the diff. Fabricating and installing the strap over the diff pinion bearing area, then secured to the cross member, greatly reduces this excessive counter-clockwise torquing and helps prevent cracking the diff housing. However, given enough pressure, anything can break.