I get those texts, emails, and mailings. They all go right in the trash. Why should you discount something someone is predisposed to buy anyway? You should raise the price instead.
If you've taken an introductory microeconomics course, you'll remember that almost all the models of a "rational" firm involve maximizing profit by picking a price point where people still buy yet will pay a maximum price per unit. How firms determine that demand curve is left as an exercise - it's assumed that firms who get it right will survive while firms that don't will go out of business, leaving only firms who get it right. This is cold comfort if you're a business owner and want your firm to get it right.
So what do the big retailers do? They A/B test. They divide customers into two groups (say, those who have a Safeway card and those who don't) and offer a different price to each. Then they measure how much of each good people will buy at each price, and presumably do some statistical corrections for demographics, the "sale" effect (where people buy whatever's on sale regardless of price), folks who won't use coupons no matter how cheap, etc. They end the sale, and then pick a different price next month. Over time, they build up extensive data about just how high they can raise their prices before people stop buying entirely.
So when you ignore the discount, that's Mission Fucking Accomplished for the store. It's telling them that the discount doesn't matter, and you'll buy regardless, and so they should try raising the price instead. They don't care about the sale, they care about the data, so that they can make more money from all their other customers.
(a) So that you do, in fact, buy them—turning that "hmmm maybe I should get this thing" into "yes, I will get this thing, especially since I can save money on it!"
(b) So that you buy them from me instead of from someone else who didn't give you a coupon. (And while you're here, you're probably going to decide to pick up some other stuff on your grocery list...)
If you raise the price too much I'm going to find myself a different store.