Sublimation = a phase change where a solid turns directly into a gas without passing through the liquid state.

This is the science behind freeze drying. Reasons that it is used include: preservation (no water, no microbial growth), creates shelf stable food, nutrient/flavor/shape retention.

Most food that comes out of our freeze dryer tastes better than when it went in. Grab some tasty shelf stable mangoes and see what I mean.