A box & whisker plot is a representation of median in a numeric variable group, where we can visualize upper and lower interquartile ranges. The line in the middle of the box shows the median, and the lines outside and parallel to the box are known as whiskers. If a point lies at more than 1.5 times the length of the box, then it is termed as an outlier.
Why do you need it?
We need a box plot to compare the numeric-variable groups of a dataset. Additionally, the size of the box depends on the variation of the group. An outlier always lies outside the box, not within it.
What kind of data you can visualize with it?
If you have a group of numeric-data of separate categories, then it could be beneficial. Assume you have a temperature of every hour in Celsius for a given day. Using a box plot with this data makes the middle line to represent the median of all temperatures. The upper and lower edge of the box will represent upper and lower quartiles, respectively. And the size of the box shows the distribution.