As a Local Guide mi goal is usually to enhance the visibility of places, attractions or businesses that may not be so well known but which I think have some special charm or significance for those who visit them.
Since these places do not usually have so many reviews, the mean score on its own gives very little information, so it is important to try to add more details to the review so that people can decide by themselves whether to visit or not. I explored the topic and looked into what other Local Guides did, but just adding more text to the review seemed insufficient. In the end I decided that a good way of conveying more information in less text would be to give partial scores.
My preferred method consists on breaking down the overall score in five separate categories, which are different depending on the type of establishment. For example in a restaurant I will primarily focus on food quality, but algo give points for quantity, service, ambient or location.
I think this kind of reviews not only helps users find places that are more relevant to their interests and needs, but it may also be used by business owners to address their weak points while continuing to be strong in what they do best instead of being left with a bad generic review.
Finally, I would like to point out the importance of second chances: of course I return to places I love again and again, but I also like to return to places where the experience was not so good (not to REALLY bad places, though) in order to confirm or correct my first impression. Anybody can have a bad day!