A final essay or another written assignment can assess students' ability to analyze or apply material or evaluate ideas. It allows students to express themselves creatively and to really show off the depth of their knowledge. These kinds of assignments are often quick for an instructor to prepare, but are time-consuming to read.
Grading essays is subjective, meaning that two different teachers—or even the same instructor—might grade similar essays differently in different situations. This pitfall can be avoided by setting up guidelines—sometimes called rubrics—ahead of time for what essays should include and how ideas should be expressed.