Sorry, what I meant was that it may be very distracting for the professor who's trying to give a lecture and answer questions while faced with a large number of lecture attendees who seem to be engaged in other tasks. Effective public speaking means making eye contact with people in the audience to get a sense of how your remarks are being received; if there's no feedback available it's likely to negatively impact the delivery of the lecture.

From the student/neighbor perspective I personally do find it distracting to have people around me doing irrelevant stuff in a context like that, but I have a pretty bad ADD so I know that's not typical of others' experience.