If the WorkSpace Performance Monitor Agent has been deployed to the WorkSpaces, it will periodically report back the server key metric statistics as defined in the Group Policy (see here for installing the WorkSpaces Performance Monitor Agent). In a large estate, this will create millions of rows within the database over a period of time. The number of days that are retained within the database can be specified here. If the number of days is too high on a large estate (e.g., 60) then it will have an impact on queries of statistics and increased disk space usage. For smaller estates, you can set this to 30 days and monitor from there.