Why is it common to salt the exterior of a baked potato?

Chefs started doing this years ago to allow the salt to absorb or draw out the moisture of the potato while baking, which results in a dry, fluffy potato. They used to do something similar with prime rib, sometimes baking it over rock salt. 

Check out the recipes below. 

Also check out this video of salt baked Idaho Potatoes from blogger Average Betty: How to Make Salt Baked Potatoes