I dislike pie charts. They have a lot of documented flaws. However some of our customers still love them, so we support them.
Question is, is there a valid use case for a pie chart sliced by date? Like each segment is a different date.
I can't think of why it would be beneficial to display the info in this format.
There are lots of discussions and guidelines around the general use of pie charts, and most of them relate to the judicious use of segments in your pie charts.
The general rule of thumb is that pie charts are best used when there is a limited number of segments in play (2-5 but less is better), and some have even used the pie in a pie chart when there needs to be more segments but they want to try and maintain the clarity of the information displayed.
So there is no rule saying you can slice a pie chart by date (as each date would be equivalent to a particular category) as long as you try and keep the number of segments to a sensible number.
By individual date is probably too granular for a pie chart, but certain ranges or periods my be useful when those are germain to be informative. For example, it may be useful to know the proportion by period (month or quarter) of sales or expenses so that a company can plan staffing or supply chain adjustments by period.
The goal of a chart is to turn data into information... that means to inform and so to answer the question that the viewer is asking.
