BO Master-Detail Report
When you use Sections in BO Report, it is called as Master-Detail report. It allows user to display the result in Section wise (i.e group wise) . It splits large blocks of data into sections (multiple blocks – group wise). Ex: You can group the data country wise, and each country block can also be called section. It minimizes the repeating values and can show subtotal as per the blocks.
In Section(Master Detail) you can have charts for each section. It is much easier to understand data in hierarchical view since the sections can be placed under each other.