This technique only counts the lead once, regardless of how many sales emails they were sent during the evaluation period. If the evaluation period is only a day of two long, chances are that most leads would have only been sent one sales email and that their open and/or clicks were for that single email. If the evaluation period is over a week long, the counts will likely not accurately represent the numbers of emails sent. For example if a lead owner sent two emails to each of his leads during the period and he has 100 leads, the report will only show that 100 emails were sent, rather than 200. The same applies to the counts of clicks and opens. You can evaluate a longer period using this technique as long as you understand that it is showing only how many leads have been sent one or more emails during the period, and how many of those leads opened and/or clicked at least one of those emails during the period.