It's also the portability with a colour-accurate HDR screen. That's a pretty huge step-up from what most laptops can do.

List of people color grading hollywood movies on their ipad during plane flights:

Steven Soderbergh has edited full feature films on a flight and I wouldn't be surprised to see him attempt to color grade them as well. Of course he's better as Steven than Peter Andrews so who knows what quality his color pseudonym would be.

Not Hollywood, but professional Youtuber's and journalists edit their videos on planes. MKBHD comes to mind.