A pie chart needs parts of a whole

A pie chart makes exactly one claim: these slices are all of something. If the numbers do not add up to a meaningful whole, the chart is lying about the data regardless of how accurate each slice is.

So the test to apply before drawing one is arithmetic rather than aesthetic: do these values sum to the total, and is that total the complete picture? Four regions that make up the entire company, yes. Four products out of a range of two hundred, no.

Pies are also hard to read beyond about five slices, because people compare angles badly. Past that, a bar chart sorted by size tells the same story better.