Very big math conferences are often structured in the following way: there are key note speakers, but also sections on more specific topics, as well as satellite workshops on quite narrow subjects. This question is about the second type of talk. Due to the size of such conferences, the talks maybe rather short (20min, 30min).
Such sections (Algebra, Topology, Geometry, Probability theory, etc.) are still very broad. The organizers might make an effort to group similar talks together within different daily sessions, but it should be taken into account that many conference participants will follow all daily sessions of one section.
How to approach such a short talk?
How to find a good balance between bringing the own results across to the broader audience without having to spend all of the talk explaining background, and saying something interesting to experts?
It seems find that in a typical 1h seminar talk it is easier to provide something for everybody: listeners who have not seen the basic constructions of the topic, and experts of the field.