on pie charts
there are countless debates about pie charts. Most arguments focus on perceptual precision: it’s easier to compare positions (as in a bar chart) than angles (as in a pie chart). Research shows that people can estimate values more accurately with an unlabeled bar chart than a pie chart. Early data viz pioneers used this to declare, "Pie charts should never be used." But that ignores the fact that pie charts are better at other things, like showing that all data adds up to 100% at a glance and showing part-to-whole comparisons.
Just a random snippet I liked from this interview
update: here's Robert Kosara making the same point on the observablehq blog
Data visualization is rarely about precise comparison, however, and when exact numbers are called for, a table is usually the better choice anyway. For other tasks, such as getting a quick but rough idea of how much a department contributes to a company’s sales, pie charts are perfectly adequate. The difference in accuracy is usually less important than the mismatch between chart and task when using a bar chart for that same purpose.