Mathematically it's simply true you don't draw less cards, just different ones. So in that aspect the consideration is to not run out of cards.
Then, given that there are cards (devotion) that can search for other cards, there is a chance you actually reduce options through discarding.
Finally, there's the access to information, which is a real and significant factor.
I'd argue that these last two should be weighed against how much you increase the odds of your targeted figure surviving the attack/how much it matters if that figure lives or dies. This is list and boardstate dependent though, so I feel it will be hard to formulate a general rule or strategy for this.