Their supported offically for software, ei you can use them without haveing to use work-arounds and hacks.
Plus you get better support from amd/nvidia ect, if you run into issues.
If you have a workplace, where lots and lots of people need to use cards for x software, haveing support could be worth the pricetag, as lost work hours due to issue = costly, and since you bought x amount of cards, amd/nvidia are likely to want to keep good relations with your workplace, thus willingness to help with drivers ect whatever they can.
If your a "normal" person, useing a home pc for a hobby... the use of such a card is basically zero.
Basically theirs like zero performance differnce, at a huge price differnce.
So unless you really need the support, theres no real reason to buy them.