"Top N Categories" option only uses number of records, which is not ideal at times.

[shane-kercheval]

For example: if you are using a pre-aggregated dataset, where each category has the same number of records, then this fails to give top N.

Another example: you have selected a numeric variable for "Secondary Variable" (or "Numeric Aggregation" for timeseries) and are either totalling/averaging/etc., the Top N Categories is still based on number of records which might not correspond to the values that are being displayed. (i.e. categories that have lower record count have higher values).