Only for an upgrade, or if it's bundled with games I don't already have and want.
I also don't keep any doubles around- everything is sold or given away in a fairly timely manner. The one exception was an extra cart-only copy of Sonic 2, becuase who doesn't already own Sonic 2 if they want it? That hung around for several months until a Sonic obsessed friend came over and told me that, sadly, her childhood copy had vanished (most likely at the hands of younger stepsiblings.) I immediately shoved that cart into her hands. "But I'm still hoping we'll find my old one!" "That's ok, then you'll have two just in case!" (I was just really glad to find a home for that game!)