Half your employees are gone, and so are half your customers. You're going to struggle for business and for staffing -- you lost the one guy who would clean the bathrooms. But you grind it out and, one delicious hoagie at a time, you somehow manage to keep things afloat. Then snap II: the re-snappening happens, and all those the customers and employees are back, standing in front of you, ready to go on in a delicious sandwich world like nothing happened.
You've ordered less flour to make the bread (and that's the most important part, no matter what anybody says), less meat, less everything. Those supply chain and staffing problems aren't going to go back to normal, but it's a small-scale operation, so you probably make do as best you can.
But what about the situation at big corporations, like agricultural giant Cargill, which is probably part of that sandwich shop supply chain? Cargill has 150,000 employees, and is a complex operation with a dizzying number of moving parts that would all be disrupted because of the snap. Corporations don't stand pat, especially in times of crisis. Those 75,000 Cargill employees who snap back into existence will find a very different workplace than the one they left -- one in which they were replaced, if their jobs weren't outright eliminated.
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Politics would experience similar problems. Most people would agree we could do just fine with half of politicians disappearing, but what happens to a newly elected senator who gets snapped bye-bye at the start of their six-year term and returns five years later? Is that person still the senator? What do you do with the person who won the special election to replace them? It's not like you can send them down to the sandwich shop for a job; Dewey from Cargill just got the last one cleaning the bathrooms.