What the "Z=0" function really does...

[TomWS]

I found this post very useful, but I still have one question.  Do you need to do this every time you repower the printer?  In other words, is this a one time setup that is remembered after the printer is turned off?  I have found that I can keep the printer running and do multiple prints with the same height calibration (including removing the bed and reinstalling), but I haven't tried printing without doing a height calibration after powering the printer on.