In order to minimize memory usage for facet counters, a full facet count is performed upon index change. For large indexes this introduces a noticeable delay. The maxCount is only needed when using packed counters, so lazy evaluation would ensure the penalty is only paid when necessary.
In order to properly guess if the result will be sparse, a full run through of the ordinal counts is necessary to calculate the number of references. maxCount is a nearly free add-on to that analysis.
In order to minimize memory usage for facet counters, a full facet count is performed upon index change. For large indexes this introduces a noticeable delay. The maxCount is only needed when using packed counters, so lazy evaluation would ensure the penalty is only paid when necessary.