Voltage Question/ATX PS

Can anyone tell me what the "+5V standby" voltage is use for or by?

I built new rig P4 3.E and Gigabyte GA-8IPE1000 pro-g, 1g pc3200 ram, etc
(my first Pentinum build)
I noticed in everast my +5v standby voltage reading is Fluctuating quite a bit, low of aroung 2.74 and as high as 5.24, but mostly around the low 3.'s
All other readings good.
In bios all voltages noted as good, exact readings are not displayed.
I have several AMD rigs none of them have +5v standby reading at all.
This is generic PS, upgrading soon, maybe even tonight.

Any thought's.
Thanks.

 

Thanks!