It's a marketing ploy that affects the race, rather than just being razzmatazz. The words are tautologies, as while "pointless gimmick" is a tautology, both words are tautologies in the statement independent of the other. After all, guys in skinsuits on ultra-sleek machines riding at absurdly high speeds... guess what you just described: an individual time trial. Yes, they get faster in team time trials, but there is nothing a TTT achieves that an ITT can't achieve, except an ITT is, you know, fair.
Besides, why does it need to make sense to a marketing man? How many people would turn up to a TTT that wouldn't have turned up if it was an ITT, a crit, a road stage? Williamp78 a couple of posts up shows it: they are going to see the Giro. They don't give a flying one that it's a TTT, because they're getting to see the Giro. Nobody who is at the race would be thinking "you know what? This sucks!" if the stage wasn't a TTT. Nobody is saying "well, I wasn't planning to go, but then I found out it's a team time trial, so I've got to be there!" There are only two things to recommend a TTT:
1) it looks cool (perhaps, but apart from a few photos, what does that achieve?)
2) it forces teams to balance their selection between rouleurs and climbers more (which is fair, but tougher rouleur stages would achieve that with less unfairness).
I'd say that the spectacle is kinda poor from a racing point of view once you get past the aesthetic of a team time trial, but then, there's not much to recommend anything in the first week of this race from that point of view, unfortunately. There is a lot that could have been done with Belfast and the surrounding area to make an interesting couple of days' racing, but not only have they done none of it, but they have actively gone out of their way to ensure that nothing interesting CAN happen.