Cardinal fan here. Our key to those coupon codes is to be signed up for the weekly email from the team. The code is the same every week, but you have to know which games it applies to.
We went to the game two sundays ago on a coupon code. The code made all tickets half price. This made it possible for a family of 4 to go to a game (in the upper deck) for about $33. We usually buy tickets in the $20-$30 range per seat and so we spent the same amount and just moved closer. I had the chance to get the 3rd base dugout seats but let them go and someone else got them (can't complain about $80+ seats for $40).
It was a good deal as the kids got Matt Holliday jerseys as the giveaway promotion AND since it was opening weekend, the kids also got vouchers for two free tickets to be redeemed by august of this year to another ballgame. So when I get those tickets (and probably spend another $40-$50 on the adult tickets), I will have spent about $150 and taken my family of 4 to two games and not sat in the cheap seats (which run about $20 for adults and $7.50 for kids)