Letting students be creative in the way they show comprehension of learning materials improves their motivation to learn. A student who feels he has to conform to the standards of, for example, a five-paragraph essay to express his thoughts on a topic is more likely to feel that he's simply being forced to do something he would rather not. A student who has a variety of options to show his understanding, and options that let him express it in his own way, is much more likely to put in an actual effort.
Encouraging creativity also improves students' overall level of comprehension of the subject material. Part of this is due to their increased motivation from having more freedom to express themselves. Another factor is that creativity requires independence, allowing students to examine topics from their perspective. For example, a student who likes art but struggles with trigonometry may be able to improve her comprehension by making cubist-style paintings and analyzing the relations of the shapes in it from a mathematical perspective.
Because students have more freedom about how they need to approach a topic when they're being creative, creativity encourages critical thinking. In a creative project, there's often no right answer, but only the student's interpretation. For example, if a student wrote a short play about Theodore Roosevelt, he would have to think critically about the different historical perspectives to characterize him properly, whether as a bullying Imperialist or a trust-busting environmentalist, or a mixture of both.
Naturally, being creative in the classroom encourages students to be creative in their lives, in the present and the future. Students who've learned through creativity are less likely to be set in their ways of looking at the world. They can see different solutions to problems that others who are only see things from conventional perspectives may overlook. Furthermore, in economies that are more reliant on technology and information, the ability to be innovative is an important skill that will help students succeed in their adult lives.