If you add a field to a chart along the X axis and it has more then 35 (or so...) distinct values, you will see the warning "Too many <field> values. Not displaying all the data. Filter the data or choose another field." While this is understandable, the ease of use of PowerView should help the user out here. As most users I have encountered are simply trying to analyze the top X results, Powerview should allow for a default sort and display the top 10 (or top x?) and lump the rest into the "other" category. This would aid with analysis in a number of ways, and the "other" bucket could be clicked on to filter a second table containing the information pertinent to see what is in the "other" bucket, while all data is now visible in the chart.