Having a summary for the grid provides a quick overview of the data in the table. It can show the total count of records, the sum of certain fields, the average of numerical fields, and other useful information. To set this up, you need to go to:
Click on a linked record field
Add field in Summary Fields
The summary for the grid can only include fields from the user table, and the values displayed in the summary are not affected by the records displayed in the grid. Instead, the values are pulled directly from the user table.