As to the PC with hard disks many don't count on the impact to the electric bill for 24x7 operation. Your average PC is about 200 Watts when running so how much is that in a year? Here it's .14 per KWH so 8,760 hours of ontime costs 245 or about 20+ a month. There may be other costs such as air conditioning.

This is why a NAS (see google) can be enticing.