Definition: two things are the same; the difference is zero
Examples:
The company is going to cut our pay, but increase our health insurance. So my paycheck will be smaller, but I won’t pay as much when I go to the hospital. I think it’s six of one, and a half dozen of the other.
If we import from country X, the price is higher, but the customs duty is smaller. If we buy from country Y, the price is lower, but the customs duty is higher. Either way, the total cost is the same, so I don’t care. It’s six of one, and a half dozen of the other.