The coupons honey applies may not always be the best deal around. Honey works with online shops to only serve you the coupons that specific online shop wants you to see, causing you to be ripped off on occasion.
Simply put, there might be a 20% off coupon that can be applied to your cart, but because Honey is getting paid by the online shop, they are only going to show you at best the 5% off coupon. This makes Honey redundant, because neither Honey nor the online shop tell you when they are working together, which is why you can never trust honey to actually give you the best deal.
Honey is getting paid by shops to only serve you the coupons that Shop wants you to see, potentially keeping you from discovering a better deal on your own.