Since eggs can only be hatched through incubators, you start off with one that never breaks, and one that will break after 2 uses. After the one breaks, you will only be able to hatch one egg at a time instead of 2, unless you buy more incubators. You have the incubator that never breaks,, because they still want you to be able to enjoy eggs, but if you wanna hatch more than one egg at a time, you'll eventually have to buy more. It just makes egg hatching easier and faster. Especially if you have a ton of Pokestops nearby, like you do at work, lol.