The use of freighter jumpseats AND upper deck seats frees up demand for seats on pax flight for all to use. As a result EVERYONE benefits.
At the end of the day we are talking about getting families together in times of high loadings eg Xmas/Chinese new year etc.
The jumpseat and who sits in such is the Captain's prerogative and, interestingly, it is a potential revenue stream that the company has yet to take advantage of.
Yes, for those of you trolling this site, CX makes a tidy profit from staff travel.