Max Group Bys

Syntax: empty, or an integer

The maximum number of Group Bys to perform during a search; the default (if empty) is to perform all Group Bys set (that are not already used in an exact-match infield query). Reducing the number of Group Bys performed (i.e. by reducing Max Group Bys) can improve search performance and reduce search load; unperformed (but set) Group Bys will have links in the output for the user to choose to expand them.

See here for more details on using Group By.