yes yes yes! (legit)
no no no! (no catch that I am aware of)
except maybe purchases made with a coupon might not count towards your insurance deductible.
We recently had to purchase prescription drugs for a little girl who had no health insurance. Internet coupons made a big big difference, and they worked. Different coupons worked for different drugs. I would walk into Walgreens with maybe 4 or 5 coupons, and they had their own codes that they would input at my request, and they were kind enough to enter codes and let me use the one that worked the best. I had $68 list price prescriptions that I paid $18 with the coupon. So, my experience was they worked and worked well. You just have to scour the internet and try a few different ones.
oh, also, different pharmacies charge wildly different prices for the same drugs, so if you really want to make yourself crazy take the coupons and visit several different pharmacies.