A piano goes out of tune when the piano is subjected to heat and humidity changes. Moving the piano does not hurt the tuning until the piano reacts to different temperature and humidity levels. The change in atmosphere affects the dimensions of the case parts making pianos go sharp in higher humidity and flat in lower humidity.
In residential use a piano should be tuned at the change of seasons. Four tunings a year is ideal. If the temperature and humidity are kept constant through external devices such as a humidifier in the winter months and air conditioning in the summer, the need for tuning can be minimized and reduced to twice a year.
In professional use the piano needs to be tuned more frequently. Usually this occurs because of increased use or an institutional atmosphere such as an auditorium that may have the heat and air conditioning turned on or off frequently. For high level professional use (like a concert hall) the piano may need to be tuned daily to insure that it is in perfect tune for each instance of concert or recording work.