Udemy supports adding a description to each lecture within a course. The question is often asked, "Should I add a description to each one, I'm not sure what the benefit of doing it would be?"
There are two reasons why you might want to consider adding them. First, search engines sometimes use all text on a page to determine relevance of a piece of text. Does Google go into each lecture description and pick up key words? I'm kinda doubting it. But it cannot hurt in adding it, right?
Second, it can be of immense benefit to the student. The lecture descriptions are visible on your course landing page. Many students will exdpand your course outline and look for keywords. I do this before I ever buy a course. I need to know that this course will cover things that I want to learn about.
So, It cannot hurt in adding them. Plus, as a final benefit. It is much easier for you to come back in the future. And 'see' what you included in any particular lecture without having to watch it.
I hope this answers your question? If so, give it a like so others might find this answer.
Regards, Robin.