My company's policy is J is permitted for 4 hours or more, for managers and above. For anyone lower than manager level, J is allowed for 4 hours or more with approval (i.e. likely yes for a TPAC flight, maybe for a TATL, unlikely for a 5 hour trans-con).

Also anyone who has to fly at least 20 round-trips per year is allowed J for flights of 2 hours or more.

The justification is similar to what others have mentioned...better rested and more comfortable employees are more productive and can hit the ground running. I can barely sleep in Y, but can easily in a lie-flat seat in J (Air Canada international J is lie flat seats)