Warm ups and exit tickets provide a way for teachers to determine prior knowledge and understanding of subject matter. This can guide future lessons in the class (i.e. if everyone knows what hardware is there will be no need to spend time on or reviewing that material).
Differentiation comes in many forms when discussing warmups and exit tickets. The differentiation can be in the type of activity/tool used such as blog post, Socrative, Google Form, etc. Tools such as a game or quick quizzes can allow students to work at their own pace demonstrating knowledge when they complete certain tasks. Polls and back channeling can allow anonymous responses - eliminating the fear of "answering" incorrectly in front of the entire class. Rotating the use of various tools gives the opportunity for each student to use a tool/s that matches his/her learning style/s.