Disklavier

Just got my MX100A.  I was reading through the manual and it said "if 
not using the Disklavier for a sustained period of time, unplug the 
cord from the outlet also (in addition to powering off)"...or 
something to that effect.  

This was discouraging since I just managed to get the beast up 
against the wall.  Does anyone have an idea of what Yamaha means by a 
sustained period of time?  Better yet, does anyone have an 
understanding of this precaution and what this risk might be to 
leaving it plugged in?  I certainly can't move it back and forth 
everytime I use it but I could put a power strip to it if necessary.  
Perhaps this is a surge protection risk and a surge protector would 
do the job.

Thanks in advance for any input.