So, the idea of defiling while memorizing, rather than during casting, was brought up in R&E and, on the one hand, I can see some value in it for a defiler… not only does it let you hide the defiling, but if you have a tree of life (or several), defiling while memorizing will let you draw on that, rather than on the local vegetation when casting.
But does anyone actually USE it?
Though my experience has been limited, I’ve never used or seen someone use Defiling when Memorizing in a game.
I agree that it removes most of the penalties for a defiler - which means it completely goes against the spirit of the class and game, IMO. So i think using it is a horrible idea (YMMV).
It’s been called out in several sourcebooks that it could be done. It’s one of the ways the VA can be infiltrated. I use a houserule that allows a wizard (Defiler or Preserver) to gather during memorization or really any time they choose (assuming they will give up an hour), however the amount they can gather and store is limited. Since I play 3e with spell points, the limit is the Int + Con bonus with a Con check. Failure results in no power gathered but instead taking HP damage.
In practice, it has been used by both types in my games, usually when we’re about to enter areas with bad terrain or when they want to be a bit stealthier.
I have never used it, as it removes most of the defiler penalties and flavor. I enjoy the look on the players faces when the vegetation around them turns to ash.