When do you use continuous section breaks?

Answer 1

Usually when you want different sections on the same page. One typical example is where you have different amounts of columns on the same page. For something like a newsletter you might have a single column for a title which will appear across several columns immediately below. Between the single column and the multiple columns a continuous section break would be put in.

Answer 2

When you want a new section, but on the same page. It is useful for things like having different amounts of columns in different parts of the same page. In a newspaper, a headline might spread across the whole page, while just under it would be a number of columns for stories. Between these you would put a continuous section break, to allow you have the two different amounts of columns.