I vaguely remember that there was a study / blog post which made a strong point against 3D bar charts. Do you have a source at hand which compares the two - 2D bar charts and 3D bar charts?
A relevant source seems to be
A Psychophysical analysis of chart readability, 2001
Sadly, I don't have access to it.
If you have an area chart, giving it a 3D-effect and rotating slightly can help readability. But I don't remember a context where you could not have used a line chart in the first place.
- PRO: Looks good (targetdashboard.com)
- CON: Values are harder to read from the axes only - you need to add values to the bars themselves (targetdashboard.com)