I've been sorting through my list of games in Galaxy, sorting them and such, and I notice that I have the ability to rate titles.

I'm curious what this does.

First of all, is this rating sent back to GOG's systems where it is used to determine user ratings? Or is this rating kept private for my own records?

If it is added to public records, are they used in GOG's systems for anything more than displaying a score? Or is there an algorithm that uses people ratings to determine what games they would be interested in? (eg, you like this one a lot but this one not as much, well then you would probably like this one because other people who like it gave those games such ratings.)

Because honestly I'm hesitant to rate many of these if they are adding to a user aggregate score, but I'd be very interested in rating EVERYTHING if it was being used in a personal score to determine suggested games.

And if it is just kept to a personal rating, well, is there anything I can do with that rating besides using it as a metric in organizing my list? (It's fine if it is, but I'm just curious if there are other features I didn't know about.)

Can no one even tell me if the rating is used for public aggregate scores or not?

just private for your personal list.
you could also create custom lists with only 5 star rated games or unrated (/unplayed) games for example