Even today in the first rapid, there was a comment (from Svidler/Giri) that early on Caruana played a move too fast, as if he was already in blitz mode, when he should have thought a bit more and found a better move.
I suspect this effect depends on who you are. Within the sphere of casual chess players, playing a lot of blitz or rapid chess will make you a better chess player across the board, and any specialisation towards the format will likely be offset by the increase in general skill. For International Grandmaster quality chess players, they're already very good, so specialisation might be unhelpful. Cf. a similar effect in Google employees with programming competitions - https://news.ycombinator.com/item?id=9324209
Interesting point. Competitive coding has virtually nothing to do with real world software engineering. But, since it's still coding, you could learn a lot of bad habits from doing it that might carry over into the real world. Better to get into <competitive hobby> instead.
