The chart I posted is an example only. Such charts are used extensively in finance and economics to show correlations between two variables. I took it from the internet. If you have ever had children, in the first year of life the health visitor would have measured the length and weight of your baby and plotted them on a curve to show if the baby was growing within parameters considered to be "normal". One axis would show weight, the other length. Or one could be age and the other weight.
In economics you plot countries' economic growth against government debt, or stock value growth vs salary of CEO for different companies to see if there is a linkage between high CEO salaries and stock value.
With investments you could plot average annual growth over 3 years for different funds against their equity exposure, for example.
What it does is to label each point so you can see which data pair the point refers to. Numbers appears not to be able to do this. The most I have been able to do in numbers is to add the two values to the data point on the chart, which in a way is superfluous since an experienced user of charts can read the values off the two axes. A label for each point would be far more helpful.