If I add percentages or values to the chart, there are no issues with either interpretation or comprehension. The pie chart is just a visually pleasant way to display data compared to, say, a table or a bar chart. Data that's displayed in a boring is quickly forgotten, but data presented in a striking way will help your point being remembered. It's akin to rhetoric/style in writing. You can write in a matter-of-fact descriptive way and bore 90% of readers to death, or you can articulate your point with striking metaphors, rhythm, etc... and make an impact.
This is an issue that I often notice with engineers. They assume that communication is transparent. A five page long table of figures? Sure! A front-end with tons of buttons, slide bars for every adjustable parameters and a full report of everything going on under the hood? Who wouldn't want that!
There's nothing wrong with pretty. You don't always have to sacrifice accuracy to get pretty. And pretty ensures that your accurate data isn't ignored.