There will always be a need for some employees. Stopping fraud & theft, discarding spoiled goods, collecting coupons, fixing the broken loop on self-checkout stations, correcting errors with wrong item or wrong UPC code that is broken, billing disputes, etc.

Warren Buffett bought a bunch of Kroger late last year. About 19 million shares at something like $26 per, so like a half-billion dollars for a company that is worth about $20, giving him about a 2.5% stake.
Kroger is the biggest pure-play grocery store. Their price to sales is crazy low because their margins are low. But the market is becoming more consolidated through all the PE roll up plays along with the strength of Walmart. Perhaps he saw more negotiating power by Kroger against Kraft Heinz and/or rising in-store shelf space rates and/or lost sales shifting across to higher margin store brand goods.