Though I'm not arguing the power consumption thing, but it might be as this is a server class machine, you have nice big PSUs to give reliability, and often they are specced for the machine to be fully loaded with Processors, HDDs, memory and cards.
If it is an older machine, the power consumption is likely to be less than a Pre-Core1 or 2 PentiumIV.
Though there are a couple of good reason using an older server class machine, firstly they are designed to be left on all the time, secondly you usually have plenty of PCI slots.
The big problem though is drive capacity, even if you have some kind or RAID card, because the drives are 13 or 32Gb, each you don't usually end up with lots of space. So if you you purchasing drives with those nifty drive mounts for your drive cage, you will normally be paying a fortune for those higher capacity SCA Ultra-Whatever SCSI drives.
Bruce S.