What are the advantages or disadvantages for teachers to use the blackboard in class?

I think there should be good and bad. The advantage is that the class is fast, and the teacher doesn't have to write a lot on the blackboard. In addition, they can play some music occasionally, which is beneficial to enliven the classroom atmosphere. But it also has disadvantages, because some students can't keep up with the teacher's progress and have no time to take notes, so the quality of the class has declined. Personally, I think that traditional teaching can be used occasionally while using multimedia teaching, and the two are combined and complement each other.