Its useful because sometimes I want to read a manga and not be influenced by the ratings (if I am). The option to hide ratings would make it a 'spoiler' type button whereby you'd have to click it to see the ratings.
You should be able to rank your top 10(or top however much needed) manga in the mdlist or elsewhere for your own interests. Basically an additional sorting method other than the usual 'ratings' and 'views' etc.