While the types of value gained through doing so vary greatly based on one's commander, Cheerios decks are often incredibly efficient and consistent, as they care less about what their zero-mana spells do, and more about how their commander is rewarding them for play so many free spells
That isn't to say the non-Inventors aren't entirely without their uses, though
10/04/04 The additional draw is separate from any other draw during your draw step
It is only the close games or those where it is all about one card where Karn tends to win
If you wanted to buy regular nonfoils in the $20 range, thats totally valid, as this card might not be an Ally, but Allies trigger abilities left and right, which you want more of
When you play cards like Farseek and Birds of Paradise, you can play your five- and six-mana cards as early as turn four or even turn three