I've been testing leaving my p5000 and p9000 to go to sleep, but not having it power down (so leaving the power on 24/7). The head seems to park adequately and the p9000 seems to occasionally wake up momentarily , sounds like it is "parking" the head then sleeping again. My p9000 auto power down doesn't seem to work anyway.
The p5000 uses 2 watts of power when in sleep mode, thats about $2 a year in electricity. Perhaps turning it off and on 100 times may require more power than that, although it may take just as much power to wake it up as it does to turn it on.
The main reason I've been trying this is powering up seems to almost always trigger an auto nozzle check, sometimes followed by an auto nozzle clean process. It seems waking from sleep does this less often (rarely) , allowing me to run a nozzle check pattern and decide if I need to clean any nozzles. Neither printer requires cleaning very often so I sort of prefer managing this myself. Unfortunately disabling auto nozzle checks in the preferences doesn't affect those during startup.
I have not come to any conclusions regarding whether or not this is helpful, other than offering a pretty vague statement that it seems to.