No, it would benefit owners of sandwich-making machines, who wouldn't have to pay for relatively-expensive labor any more. The owners themselves would have to be wealthy enough to afford the machine in the first place. The effect would be to centralize wealth further, as the owners of capital get more money, while those without capital are left unable to make money through their labor.

You're right, but that's done by providing value to the payer. In this case, cheaper, faster food.

Exactly. And it would be more popular in countries with higher labour costs (e.g., Australia).