The Pie Chart is a primary chart type in Excel. Pie charts are meant to express a "part to whole" relationship, where all pieces together represent 100%. Pie charts work best to display data with a small number of categories (2-5). For example, survey questions in yes/no format, data split by gender (male/female), new and returning visitors to a website, etc.
Pie charts should be avoided when there are many categories, or when categories do not total 100%. The human eye has trouble comparing the relative size of slices in a pie chart, so pie charts should also be avoided when slices are similar, unless similarity is the point.
Simple, compact presentation
Can be read "at a glance" with limited categories
Excel can calculate % values automatically
Difficult to compare relative size of slices
Become cluttered and dense as categories are added
Pie charts are one of the simplest chart types in Excel, good for showing "part-to-whole" relationships with data in a small number of categories. Pie charts get a lot of criticism in the professional data visualization...