[Jac Mac]

As long as you continue to run U-joints in an IRS setup that adopts unequal angles in the UJ's at any point in the suspension travel when under acceleration load you run the risk of failure in the spider gears or splined stub output shaft from the diff, further to that if the halfshafts are light enough in construction/material that the UJ's can get out of phase due to twist then the UJ's are also likely to fail along with increasing the amount of load the stub shaft will experience.

Half shafts that use CV's are actually able to twist like a torsion bar without inducing the mechanical bind that occurs in UJ types.... essentially acting like a shock absorber in the driveline.