As someone that works in the food industry I can tell you that in supporting that method of checkout you are going to make the retailers very rich. Once you fire up the retailer app and start scanning items, you are going to be a walking gold mine of data. Your exact location in the store is going to be logged, how much time you spent in each aisle and in which quadrant within that aisle you stopped and spent time scouring the selection. Add all that information to your basic identity metrics, throw in frequency and a couple of other time based data points, and the retailer in question will be able to sell that data all back to the manufacturers and suppliers. All of the major grocery retailers already have reporting mechanisms that the various suppliers can opt in and out of, and they already pay huge sums of money for it, but right now its all pretty simple and all just based on number of facings, sku count and sales. All of the added information the retailers would be able to sell with app based check out will be an absolute gold mine for them.
Someone like Loblaws will be able to sell data to a company like Coke that will indicate age, gender, historic buying preferences, time spent in the soda aisle, when and where the consumer stopped within the aisle and which sku they were looking at, where Coke's product is placed in relation to the product the consumer stopped to look at, what is in their basket at the time of grabbing that 12 pack of Coke, etc, etc. They will also be able to trigger coupons and promotional items, based on what's in your basket, and then pit the suppliers against each other. So during BBQ season, if someone picks up and scans 12+ hamburger buns in bakery, a coupon will trigger in the app alerting the consumer that Coke is offering $0.50 off each 2L with the purchase of 12+ hamburger buns. Loblaws can then see if there was a sales lift tied to that promo and turn around and approach Pepsi and tell them that Coke ran this promo tied to hamburger buns during the BBQ season and show the lift %. Pepsi will want in, and now you have both Pepsi and Coke fighting over price reductions, all which benefits the retailer.
Use app based checkout at your own peril lol.