The Search Results Grouping controls allow you to control on a search query how many qualifying documents from an index to compute before trying to sort and rank them to find the top k results (here k is usually 10). In a multi-queue-server setting the query is simultaneously asked by the name server machine of each of the queue server machines and the results are aggregated.

Minimum Results to Group controls the number of results the name server wants to have before sorting and grouping of results is done.