It's not required. I wire the DA-2 trigger cable to ground, so the brick is on all the time (as most bricks are). I usually use a power strip though, cutting power to everything. But sometimes I forget to flip the switch and the stuff remains on. No problem.
And finding good bricks in Sweden is a pain.. The DA-2 has pretty good efficiency but it's very large and powerful. Overkill in most cases.
I eventually got a DA-1 on Ebay.co.uk instead (£13 including shipping). Cheaper than DA-2 and should be more than enough. I have to say that thing was built like a tank despite "only" being 150W.
Some DA-2 are known to make a squeaky noise if no power is drawn when turned on. This would take care of the problem.
Returning the DA02 to standby mode would also eliminate whatever concerns one may have regarding leaving the ATX 12V rail on when the computer is turned off.
I see. My DA-1 does whine ever so slightly, but it seems to be about the same regardless of whether it's on or off. I haven't soldered the Mini Fit Jr molex yet so I don't know if it'll be worse under load. I sure hope not.