It isn't very detailed (not as much as a stem and leaf plot or histogram), but it can be useful for showing if there are potential unusual observations in a given data set.

Basically, box and whisker plots are used to graphically showcasing groups of numerical data through their quartiles. They can also have lines extending from the boxes that indicate variability outside the upper and lower quartiles.

Box and whisker plots is valuable in presenting multiple data sets that come from independent but related in some ways to each other sources, e.g.:

• scores of tests between schools or classrooms
• data describing "before" and "after" a change had been made
• data from machines manufacturing the same products