I once stood at the grocery checkout and casually glanced at the receipt of the person right in front of me.

Seeing that they paid $12 more than I did for the same items surprised me a bit.

The reason was simple. That person hadn't clipped any digital coupons from the app.

These days, large grocery stores don't give out paper coupons; they keep them in the app. You need to clip them in advance for the discounts to apply automatically at checkout.

Just looking at the Kroger app, over $600 worth of new digital coupons are added each week, and you can clip up to 150 at a time.

When combined with weekly sale prices, it's common for the total in your cart to drop by 20 to 40 percent at once.

The problem is that if you don't clip these coupons in advance, they won't apply automatically at checkout. Only the sale prices will be applied, and the coupon discounts will be lost.

In fact, studies show that 43 percent of shoppers forget to use the coupons they've clipped when checking out. Even with the app open, they miss the crucial moment to tap and end up losing money.

It's not just Kroger. Smith's, Albertsons, Walmart, and Target all have their own coupons or circle offers available in their apps.

About 45 percent of American adults use the loyalty apps of their frequently visited grocery stores, meaning nearly half of the population is already in this game.

However, there are still many who download the app but never check the coupon page.

Data shows that 71 percent of digital coupon users save at least $10 a month, and 36 percent save over $25.

While it may seem like just the cost of a month's worth of coffee, when you stretch it over a year, it's enough to cover several car washes.

I believe that driving a nice car is great, but being precise with your spending is what really matters. You can live extravagantly, but you need to manage your wallet to sustain it.

Personally, I don't just use one grocery app; I have apps from two or three of my favorite stores. It's fun to compare which one has the best deals each week.

If you add a cashback app on top of that, you can get money back on the same receipt. Coupons and cashback often don't overlap, so using them together is usually fine.

Local Korean grocery stores are also starting to create their own apps or text coupon services. Many people miss out on Korean grocery coupons while only focusing on American ones.

When I bring this up in gatherings with friends, the reactions can be surprisingly varied. Some have their app notifications turned on and clip coupons weekly, while others haven't even downloaded the app.

The difference between the two may seem trivial, but when you look at it over a year, it adds up to a significant amount.

Coupon expiration dates can be surprisingly short, usually ranging from a week to a month. It's common for clipped coupons to expire before you use them.

So, the method should be simple to maintain over time. Just invest five minutes before you go shopping to quickly browse this week's coupons and clip what you need.

If you set a specific shopping day and make it a habit to organize coupons the night before, you'll definitely reduce the chances of losing money at the checkout.

For seniors who aren't familiar with smartphone operations, more stores are now allowing you to simply tell the cashier to apply the coupons, which is worth noting.

It's great to live confidently, but if you're paying money you don't need to, that's just a loss.

If a few taps to clip some coupons can save you several dollars each week, isn't that a smart way to shop?