I NEVER use it... I never reach my credit card max on my other card, I pay it off completely every month, so my discover card just sits in a drawer. It's not hard to leave it open if it helps my credit, just seems kinda useless. This stuff is like a second language to me tho, so if you say keep it open, I will! Thanks!!
FTR, you must use it even for a small purchase every few months or so to ensure it is not closed by issuer for nonuse.