Put Coaching Into Practice

I would like to know more about coaching because I have never had a coach as a teacher. I could have probably used one. I wonder how much coaching gets done because I would assume teachers feel like they don't have enough time in the day. I think it is a great idea to have the Principle serving as a coach and giving feedback about what he/she witnesses in the classroom. I wonder how many Principles take time each day to go into the classrooms and witness what is going on.