Serves those who are hearing-impaired. Relies on outside power source. Ability to answer questions based on the lecture-if presentation is live. Serves those who are vision-impaired. Video and film can be sent almost anywhere in the world, like distant learning.
Cost is relatively cheap.
Serves those who may be hearing-impaired. Mail-in replies may be required. That is not very time effective. Assumes all have access to a VCR or a film projector. Must supply printed materials as needed.