The supposed advantage. Many perfectly productive languages don't even offer the option to specify the type at all, and not just in the inference case. As far as I'm aware, nobody has ever convincingly demonstrated (with empirical data) that this is worse along any metric that people care about (development speed, bugs, cost, etc.).
A lot of people have preferences on this front. Somehow, these preferences get promoted to best practices if not moral license. Just, which approach is claimed to be better really depends on who you ask, and then mainly on whichever language that person first cut their teeth on. And nobody's going to be able to cite any well-designed study that demonstrates their preference is actually superior, because none exist.
