Like all language skills, writing skills atrophy when they aren't used. Yet our students often report that they do no writing at all during a semester because they don't even take notes during some classes. For students who take only multiple-choice exams, writing can be avoided almost completely for months at a time. Assigned writing in all courses helps students keep their writing skills sharp.
Moreover, faculty in all disciplines have discovered that assigning writing in their classes helps students learn material and improve their thinking about ideas in the courses. Writing assigned across the curriculum also helps students prepare for the day-in and day-out communicative tasks they'll face on the job, no matter what the job is. Equally important, student need to learn about how writing is used within a discipline, and many kinds of assignments give students practice with disciplinary forms and conventions.
So why assign writing in your classes? Students will learn more and will leave the university better prepared to face communication challenges if they write consistently over the course of a four-year college program. Specifically, students will learn more about the material in your courses if you assign writing for your courses.