William Playfair was the precursor of using the series plot. He was one of the first to present statistical data on charts. He designed many ground-breaking methods of data visualisation that became popular with time thanks to how clearly they provide key information. A good example is the figure below, showing foreign trade data for North America over several dozen years.
Figure 1. Foreign trade balance for North America by William Playfair.
Source: Playfair W., 2005: Commercial and Political Atlas and Statistical Breviary. S22.
Today, you do not need artistic talents to prepare just as interesting data visualisation. Below you can see a simple series plot form with only one variable on mean company expenses in individual months.
The chart below shows data on average income in a year and has some additional elements.
Individual quarters are shown in different colours, which helps the reader notice income in individual parts of the year more easily. Additionally, the vertical lines mark important business events that could affect the presented data. In this case, the lines represent starting dates of broadcasting company product and services advertisements. An analysis of the chart reveals two significant increases in the second and fourth quarter. Both were preceded by advertising campaigns, which could be considered factors contributing to the improved income.
To sum up, the series plot is a good choice when you need to show a trend in data in time. Additional elements in the graph (such as markers or colours) help present auxiliary information.