It is not a good idea to take the stem off the pipe every time you smoke it as you may crack the shank, especially when the pipe is still a little warm from your last smoke. Stems shouldn't be taken off the pipe unless you are going to give the pipe a good periodic cleaning which depends to a extent on what type of tobacco that you are smoking since aromatics require more cleaning then English blends because of the casing on the tobacco.
I usually only run a pipe cleaner through the pipe after every one or at most two smokes. However, I usually never separate the stem from the shank unless the pipe is a bent and I can't run a pipe cleaner through the stem and the shank unless the two are separated. I usually give my pipes a good, thorough cleaning with pipe sweetner or cheap vodka, stem cleaner, Quetips and pipe cleaners after about 15 smokes. I do not buff the outside of the bowl since I like a patina from the oils of my hands since the briar looks more athentic. I only buff about once a year because if you buff too often and don't do it right your can buff off the name, model number and date code if there is one.
That being said, everyone is different about their pipe hygene a similar to how many times we wash the car in a month.