i've found, even at the one school, it varies a lot.
Depending on which instructor, how busy they are, when they last had time to eat, etc
I don't book in with instructors who don't give pre flight briefs. I'm paying to learn how to fly, not to sit in an aircraft. My beleif is that the air is for practical, the ground is for theoretical.
A pre flight breif should, at a minimuym, be where the student and instuctor go though the purpose of the flight. Even if it only takes a few minutes, theres no reason to fly if there is no purpose to the flight.
As for post flight briefs, i think they are just as important. At a minimum you should be made aware of what you should do next, what to focus on and any feedback, good or bad.
If an instructor doesn't think these are needed they shouldn't be an instructor