Most reports that surface the checkbox "Require Sales to be Placed by the Selected Reps" operate by reporting across all "accessible" accounts to the selected reps. For Admin users, it effectively means "all accounts" since an Admin can access all Accounts.
This is very much intentional as 99% of the time, the use-case for running these reports is to surface "historical" sales. For example, if Rep A takes over accounts from Rep B then when Rep A runs sales reports, they absolutely should be able to see the sales from Rep B a month ago, etc.
For example, when RA1 is run only for an admin user, you'll see sales/records for sales that are not that user's per se. But they are surfaced because admin users have implicit access to all Accounts. Checking the box "Require Sales to be Placed By Selected Reps Below" does have the effect of applying the criteria of "ONLY show sales for this set of sales reps."
 
Let's look at an example:
1. Let's say you select Rep = John and you DON'T check that "require ..." option
2. The report logic is: grab all sales in the date range attached to ANY account that is currently assigned to Rep = John
3. This means that if John took over ACME Bistro and there was a sale done before under Rep = Alice -- that transaction would be included. Even though John didn't make it
4. However, if you were to check "require sales..." it says: please ONLY report on sales ACTUALLY linked to John. I do NOT want to see Alice's sales for this same account
 
If you do not see this option on a report, then it means that Point #2 is implicitly used, and the logic is showing inherited sales.