It seems like an interesting way to combat decks full of trinkety artifacts, which only seem to be getting more and more popular, though the specific interaction against Smothering Tithe is pretty hilarious
It is the constructed cube decks where Karn really shines
DArgenio writes at Escapist Magazine, others have suggested cutting down the data to just one card type at a time, such as creatures, which should help the network recognize patterns and even flavor among them
Plus some decks, like Hollow One, specifically need discard spells
The sets blistering sales numbers reflected this love and then some
Protect a creature from the color of your choice, and draw a card for your trouble