I've been doing affiliate marketing since 2000 - when it really was a good solution for banner space (those things that used to get clicks) from smaller publishers long before a thing called Google came around.
Now, candidly, I see it mostly as a pathway for parasitic marketing - with little to no benefit to you.
Coupon and deal-site Affiliates will bid on your trademarks (even if you prohibit it) - and fight for your own organic SEO. Now, depending on what you sell, you might like getting a bunch of traffic from someone like retail-me-not, but keep track of how many customers are 'new' versus saw your coupon box and search for a coupon - used it for a discount, and then you paid a commission for that sale...?
For us, we do it - but we try to focus on review sites; odd-sites where you never know where the traffic comes from; and then yes, discount and coupon sites - because we get more new customers than for what we eat on customers (I call it "round-tripping") being on your site, finding a discount code box, and then searching the web for a deal.