If nothing else, the logistics of transporting J&J make it a lot better in a lot of cases. Pfizer in particular needs to be transported super-cold, and Moderna needs to be frozen as well. J&J can be handled much more like a flu shot.

That said, I'm smarting a bit (even though I understand why) that the fully vaccinated guidelines cover 2 weeks after J&J, while it's looking likely the mRNA vaccines give you better protection even 2 weeks after the first shot. (You really do want the second... the 6-month Moderna study shows you get about 10x the antibodies from the second one, which means the protection lasts much longer if nothing else.)