Failure to provide an adequate number of questions using open ended questions fails to challenge the student and incorrectly assesses their ability. Now here is another thought. Most students want to be challenged. It gives them a sense of positive reward or feedback to answer questions correctly and can also be a motivational tool. Questions allow the instructor to continually adapt the material and level of the lesson to better meet the students needs.
Some students do better with practical examples while others do better with definitions.
By questioning students and seeing where their strengths and weaknesses are one can provide better educational material. In addition some concepts or examples are not effective. Some questions are too difficult, too confusing, too ambiguous, and if put on a test, do not measure the students true knowledge but only reflect that the question may be confusing. Fine tuning lessons can be very important. Finally, to teach is to learn.