Im not sure how it effects the quality and longevity of the output of the psu though. That is my question.
I found another link on ebay for powering older AT P8/P9 boards with modern eps 24pin psu.
They had a 3.3v 10watt load applied to the connector along with an on/off switch and AT P8/P9 connectors.
So that is where the question is originating from. Maybe you can power the gridseed, but only the 5v and 12v outputs being used.
Is there a risk of not using the 3.3v output with just any psu you buy intended to go into a pc?