[bitwize]

Pie charts are useful when there are large disparities between some of the data items. Like, here are our total expenses for last year, we spent 6% on administration, 14% on facilities, 11% on R&D, 33% on manufacturing, and 36% on sales and marketing. You can see at a glance, even with human eyesight's poor judgement of areas, what the dominating two expense areas are. Or, you know, here's a breakdown of the OS our dev team members use: 85% use Windows, 11% use macOS, 3% use Linux and 1% use "other".

Oftentimes they will be labelled as well with the exact percentage numbers which helps. It's not really a scientific visualization tool, but it adds punch to a presentation when you want to show that one or more subsegments of a whole really dominate the rest.