I always teach transparently, although I had not thought of it in those terms before. I believe it is crucial for students to know why I use the methods I use and why they are performing each exercise or assignment. They need to know that the assignments are valuable, why they are doing them, and what they are supposed to learn. I always receive positive feedback on this - not just from students, but also from observations by other faculty and during teaching demos at interviews. I can't imagine not teaching in this way. Part of it is due to my personality - I am one of those people who has to know how things work, what the plan is, the big picture, etc. I am not happy to simply do what I'm told without explanation, and don't expect my students to be either. In fact, I actively encourage them to question the education they are receiving.
Very insightful question, OP. And I particularly like Dundee's response on both personal and pedagogical levels. I think transparency is especially important in skills based courses such as composition because there are so many techniques to get to a skill but those techniques so easily get interpreted as rules by students. And so the student incorporates the techniques as norms, confronts yet another teacher with different techniques or a lack of patience for rigid frameworks, and voila we end up with the impression that good writing (for example) only means "writing for
this teacher."
I try to address this issue in my classes by distinguishing between the end goals and why I am requiring a particular approach to a paper. I readily identify a few of my idiosyncratic hot buttons (eg. rhetorical questions, over use of "you") and why
at this juncture I want them out of the writing. When a student says that they always learned "every essay has three main points," or "every paragraph is five (or seven) sentences" I answer in terms of what I assume was their prior teacher's point was and how we are now working with that goal but beyond that constraint.
Then again, you do want to be judicious. You don't want to over burden the course with too many provisos, do you? Oops, just broke two of my rules.