There is. LHF emails you if you don't use your tickets, and asks that you either list them for sale or let someone else use them.
I try to use as many of my tickets as possible, and I give them away to friends/co workers when I can't got. But the reality is, there are games I can't make that I can't even give tickets away to (midweek games, early season games when the weather isn't as good, etc.).
If I can't go or can't give them away, I do usually throw my tickets up on Seat Geek for about $10 bucks so that someone can get in the door for under $15 a ticket after fees, but I don't do it until a few days before the game most of the time. So go look online if you want single game tickets, GA tickets can be had for like $10 right now and seats like mine (under the awning) are going for ~$20 each after fees for the home opener, and even less for the next weekend series.