Whether I read a function name or comment personally that does pre occupy my mind and sets the mental frame for what comes next. If the comment or function name say doX() or //this does X then I expect it to do that but need to be on the lookout for whether it actually does that.

With a function though I can easily step out if this part turns out not to be interesting, I can easily step over it next round if debugging, I don't need to keep track of where //this does X ends etc.

Of course none of these help if the previous author was really bad at what they were trying to communicate. They can both implement doY() in a function called doX() and have //do Y code run in with //do X for example by interleaving statements for both. If we assume we'll intentioned authors for both though, I would tend to see more pros for structuring code with functions than via comments.