I believe I have definitive evidence from my day job... If you are after hard drive reliability leave it on 24/7.
In my industry the burdened cost of labor is $340,000 per 1800 hours, the cost of electricity is insignificant, the cost of a hard drive is insignificant, the cost of a computer is insignificant... the cost of lost productivity is astronomical, the cost of lost Intellectual Property (IP) can bankrupt.
If you are after maximum reliability, keep in mind that backups are an integral part of quickly restoring capability. To achieve that we require all lab computers to have a ups, dual hard drives that are cloned weekly, and all IP backed up twice, with one copy stored in another secured physical location. Hardware is replaced every 3 years maximum.
In my industry the burdened cost of labor is $340,000 per 1800 hours, the cost of electricity is insignificant, the cost of a hard drive is insignificant, the cost of a computer is insignificant... the cost of lost productivity is astronomical, the cost of lost Intellectual Property (IP) can bankrupt.
If you are after maximum reliability, keep in mind that backups are an integral part of quickly restoring capability. To achieve that we require all lab computers to have a ups, dual hard drives that are cloned weekly, and all IP backed up twice, with one copy stored in another secured physical location. Hardware is replaced every 3 years maximum.