mine usually runs 24/7, doesnt effect energy consumption much either way.
I believe the PSU is capable of handling the long usage, i mean the system is practically server grade' meaning always on mode - and its more than capable of handling that.
the fact that it draws more energy on every power on and cold boots, unless theyre infrequent cause heavy impedence on the system ... though theyre able to handle it otherwise it would be clearly noted "DO NOT TURN MACHINE OFF/ON EVERY SO OFTEN ETC ETC"
the technology is so advanced now, its safe to leave them running.
you may benefit from just putting it into sleep mode then pressing a key to wake it up, generally gives the hardware and circuitry a flux power draw and doesnt stress it too much.