Sales Summary by Principal
This section shows the totals for each Principal (no details).
Sales Summary by Customer
This section shows the totals for each Customer (no details).
Only customers who have purchased in the current date range will show in the Customers table, which distinguishes the active accounts from the inactive accounts. Also for this reason, the year previous totals and "% Diff" may not match between the two Sales Summary sections -- Sales Summary by Principal indicates to sales for the previous year, including inactive customers.
Use this report to get a year-to-date overview of the sales rep's business versus last year. If more details are desired in either the Principals or Customer areas, use the Sales Summary report to select and generate a report with the desired detail level.