It is a fact that turning an electrical appliance on puts more stress on that appliance than keeping it running for a long time. The reason is that the initial surge of electricity through the circuits is a traumatic event (shocking, even). Your computer is an electrical appliance, and therefore constant power ups and power downs can wear out the parts before their time. If the durability of your hardware is an issue, then leave it on."
Kind of like a car. Most people don't realize when you accelerate hard, or when you stop and go at a stop light, you are doing the same thing. It's always that initial surge that messes everything up. Lots of stress. Stop and go constantly in a vehicle puts quite a load of stress on the car's engine and transmission.
Lots of mixed opinions. Let's just keep it on all day if we're going to use it, then power it down at night. If we don't plan on using the PC, don't turn it on then. Unless if they are servers. If compnents fail, we'll just have to buy new parts for it. PC's will eventually fail, but that gives us excuses to buy a better component, right? hehe
Today is yesterday's future....