I am a novice brewer and have 5 brews under my belt (and 3 in my stomach). Three of the five brews came with specialty grains that required steeping up to 170 F. I believe your question has to do with mini-mash brews that require you to mash the grain at certain temperatures. I haven't expanded to the partial mashes or all grains yet (but intend to do so in the future) but specialty grains that require steeping are used to impart tastes and colors to your brews. Mini-mashes are done to increase the sugars available to be converted into alchol and CO2.