This is the continuation of a previous post.
The lower temperature rests in a step mash deal with hydration, mash pH, proteins, and beta glucans. They are not needed with most fully-modified malts, but work well with undermodified malts or home malted barley. Two of the three remaining rests deal with the degradation of carbohydrates — how starch is broken down into a mixture of fermentable sugars and unfermentable carbohydrates. These rests can be performed regardless of the type of malt you are mashing.