I'm a fan of mechanics, and particularly mechanics being known to the players. They help me quickly decide what I'm doing and how, without having to ask all sorts of probing questions to tease out what I'm allowed to do, while everybody else waits, or worse, checks out. They also help the DM figure out how to resolve things quicker. On the other hand, it really gets my goat when I go to the trouble to learn the mechanics, so that I can participate efficiently and effectively, and the DM ignores or changes them from moment to moment, which I've also had happen in several games.