Coupons have two purposes, which seem contrary, but are essential to understand how coupons are a form of advertising:

1) Saves you money (versus the retail price of the item)

2) Makes you more likely to buy the product on the coupon.

Your use of coupons adheres to both value #1 (saves you money, because you know what's on sale) and value #2 (advertises products on sale, increasing your chances of buying them). This is the core advertising model of coupons and why they've been popular forever.

This automated use of coupons saves you money if you happen to purchase an item for which a coupon exists, without requiring you to do any extra work to save that money — but also without having the desired advertising outcome of making you more likely to purchase that item.

This compares well to adblocking. Internet advertising on websites:

1) Saves you money (versus subscribers-only paywalls)

2) Makes you more likely to buy the product on the advertisement

And in that analogy, ad-blockers are directly equivalent to coupon auto-adders: they allow you to save money without having the desired advertising outcome of making you more likely to purchase that item, in a fully-automated manner that doesn't require you to exert any effort doing so.

Coupons are a precursor form of advertising ("pay-per-clip" :) where you are paid money to view the advertisement, and are more likely to commit to buying the product when you 'clip' the coupon — it's a marketing psych thing. They also have perfect tracking, since retailers provide coupons to manufacturers along with purchase date and location.

Coupon autoclippers break that agreement, such that you're 'paid' for being influenced by the advertisement without ever having been influenced. The coupons are no longer valid for tracking the effectiveness of advertising A/B tests in different markets (your Safeway account's zip code is surely part of that data). They are no longer proof that you viewed an ad at all.

You're not wrong that this app would ruin how you shop quickly, but you're also shopping quickly using a list of products that were predetermined by Safeway and/or other marketing divisions to be of maximal interest to them for you to purchase. As long as you're okay with that, coupon clipping is an excellent approach. For others, autoclippers would minimize the price paid without changing their purchasing methods (which may be paper-based, brand-focused, or random-chaotic)