One to supply the motherboard with power. ATX, EZ and the 4 pin ATX.
And the other PSU supplies the optical drive, floppy drive, hard drives and the blowers.
Eventually the latter PSU will power the water cooling feature.
Some might say 'overkill' but the extra PSU was just lying around doing nothing, I have a case that accepts 2 PSU's, water cooling in the future & I like tinkering with stuff like this. Oh, and I wanted to keep the Mobo power completely separate from the drive/fans supply.
I brought a 24 pin ATX extension lead and a 20 pin female ATX plug (to connect to the secondary PSU) and modded it to switch the 2nd PSU on when the Mobo PSU starts.
It's running sweet