While linguists argue first and foremost for a descriptive approach, there is an argument to be made that there is a place for both description and prescription in language study. For example, when adults learn a foreign language, they typically want someone to tell them how to speak, or in other words, to prescribe a particular set of rules to follow, and expect a teacher or book to set forth those rules. But how do teachers know what rules to prescribe? At some point in time, someone had to describe the language and infer those rules. Prescription, in other words, can only occur after the language has been described, and reasonable prescription depends on adequate description.
Descriptive and prescriptive grammar often clash instead of collaborating. Descriptive grammar explains how people actually speak/write; whereas, prescriptive grammar dictates how people should speak/write.
I use descriptive grammar in my everyday writing but i also try to be prescriptive as well.