1) Deals are not good. That is, the price reduction is not real or comes with reduced service.
2) Problems with honouring the purchase. The experience is not as purchasing something at reduced price from the shop, you need to go through separate process and the vendors act as if you forced them to sell you the deal. Some try to upsell a bit too hard, degrading the experience if you refuse. Some claim that your coupon is not valid and you need to deal with customer service to resolve issues.
3) Social stigma. It's uncool to take someone somewhere with a coupon, so all the deals for two are not good.