Cold is usually seen as a lack of heat, but that is not completely true. Cold can be used as an element of its own, and skilled sorcerers in fact do use it that way. It is much more difficult to master cold than fire, but the effects can be quite devastating, as this spell often shows. Because fire is easy to control, many creatures developed some level of resistance against it, but with deep freeze, sorcerer can fight even such monsters quite effectively, without wasting lots of precious mana on powerword kill.