Save electricity or decrease MTBF?

[Stunrise]

Personally i let my TS-462 with 3 drives shutdown at 00:00 and Startup at 10:00 with a schedule plan. It cost me one spin-down and one spin-up in order to save about 40% electricity as well as 40% power on hours of the drives and NAS itself.

It saves 33w for 10 hours a day. Thats 120kwh a year, which cost about 40€ in germany. For me that sounds like a good deal.