Itch will never tell. Precisly because people will try to abuse the system.
Ratings do obviously what you observe. They appear to your followers, wether you include a review or not. They get culminated in the rating score wich is displayed on the game page, if ratings are not disabled alltoghether. And by black magic there is a ranking on top rated games and in game jams to have a weighting, so as to not put 1 5 star rating game above the game with 99 5 stars and 1 4 star rating.
Since you cannot read bad reviews and determine why people dislike a game, for many games they are actually useless. For example, games with AI art get hate-ratings. The most a player can take away is the absolute number to deduce, if a game is at least somewhat popular, but comments do that as well. And even that says little. Some players do not rate at all and some type of games do not get many ratings at all. Maybe for fear of screwing your recommendations.
Oh, and of course it should influence what games are recommended to you, based on similar players.
Search, as far as I know, is random and truncated. As positive ratings would not increase accuracy nor relevance, I doubt they are included.
And you should be aware, that "prioritizing" ratings in any way can result in bad consequences. It is by definition not a thing you can prioritize, so any means you could have actual influence would be some sort of review bombing. And I am pretty sure there is some point in the faq or tos forbidding such actions.