Have you ever been inadvertently sprayed with water as you reached into the vegetable bin at the grocery store? What's the point of spraying fruits and vegetables, anyway?
It helps keep them fresh. See, in their natural state plants replace water they lose to the atmosphere by absorbing it through their roots. When plants lose more water than they take in, they wilt and eventually die.
In the grocery store, plants have no way to absorb water naturally from the ground. So they need to be sprayed to keep them from wilting.
Some vegetables, like onions and potatoes, don't need to be sprayed because they have skins that are good at keeping water in. But a vegetable like lettuce loses water at a faster rate, so it needs to be sprayed pretty often.
The same goes for fruits. If you skin an apple and leave it out, it'll dry up and shrink a lot faster than an apple with the skin left on.