This is the behavior we are trying to nurture. If you begin to talk at too high a level, students will stop understanding and thinking, and will ask no questions. Questions tell you whether your class is asleep or awake. If encouraged, students will ask questions about concepts they do not understand. These questions give you immediate feedback when you are unclear, and tell you where you need to spend more time.
Education is a dialog between student and teacher.
It is not a monolog - if it were, students could simply buy the textbook and read it themselves. Students attend classes so that 2-way communication can occur. Questions are an important part of this dialog. For all of these reasons, questions should be actively and constantly encouraged. There are a number of forces at work to discourage students from asking questions.