The unit is a little warm to touch when leave on all the time. Should I turn off when not in use?
A bit warm to the touch is okay for almost amny electronic equipment. For Solid State equipment, as long as it does not get hot just sitting idle it is better to leave it on rather than power cycle it. Heat cycling and startup current surge are both cause equipment degradation. Of course, this is an issue with my environmentalist side, but I try to compensate by selecting equipment with lower idle power consumption where possible. 
Tube equipment is a more difficult thing to decide. Heat cycling and startup current surge are still deleterious but tubes degrade with power on hours. Here, I might consider a variation on the rule I give people when they ask me about turning their computers off: For computers, I suggest trying to turn them on only once a day. If you think that you will be using it later in the day then leave it on. If you turn it off and thing ‘dang… I probably will be needing it later’ then turn it right back on before the capacitors discharge any further and before it cools down any further. For tube equipment, I might consider using a similar rule but I am not sure of the time constants. Surely the once a day rule still stands, but I do not know if it is better to turn it off or leave it on for tomorrow. It may be better to leave it on for the next day but not two days later… This gets to be a gray area. Cetainly tube lifetime is reduced if left on continuously but when to power off is a bit less clear.
Yes, I know… Long answer for a short question, and you did not mention tubes. I figured that the long answer may be good for general public consumption. Discussion is always welcomed.
J.P.
I would leave the PPP on all the time. As JP suggests you have to pay attention to what it is you’re powering, they all would not get the same answer, but as far as the PPP is concerned, leave it on.