Plot graphs are helpful when you want to show the relationship between two or more variables.
For example, a bubble graph can show you the relationship between two product attributes (say, sweetness and texture) and how they relate to price. In such a graph, there would be a bubble to represent each brand. The score of each brand on sweetness and texture determines the bubble position in the chart. The price of each brand determines the size of the bubbles.
Plot graphs are the default visualization when you have two or more measures across in your analysis.
In an analysis with three dimensions across, the first column (excluding the total) is represented by the x-axis; the second is the y-axis and the third is the size of the bubbles. Each bubble represents a row.