Well leaving it in standby won’t harm the PS2 at all but there is one minor thing you might want to think about. The power supply unit (PSU) in the PS2 just like any transformer is producing the potential of electricity to be used at any time, thus a small current draw, in turn wasting electricity. Unless you cut the power to the PSU with the switch on the back the PS2 will actually be sitting there wasting electricity, not much at all though, but really, it not like its hard to just reach back there and turn it off.
Remember the PSOne; it had the wall mount PSU that when it was plugged in to the wall regardless of if the PS1 was being used or not it created heat. This was because it was creating the potential of electricity to be used, this goes for any other wall mounted transformer, regardless of if the unit it supplies power to or not is in use it’s sitting there burning up electrons.
Just my thoughts, no big deal really. JUST TURN IT OFF. Or Arnold might start those damn rolling black outs like Gray Davis had us Californians go through last year. LOL
