For every campaign sent (e-mail and SMS text messags, survey and event invitations) detailed reports are generated and stored in your account. These reports are dynamic, and continue to be updated long after the initial campaign is sent. Reports include information such as:
You can use these reports to judge the effectiveness of your campaigns, and in coordination with your Google Analytics account to determine how many e-mails have been converted into goals achieved!
Site Caddy message reports are formatted in an easily readable style, and include graphics to represent key areas of data.

A clean recipient list is a list with accurate information and should not include invalid, inactive or opt-out addresses. Sending e-mails to invalid addresses is a sure way to get flagged as a spammer by mail servers.
Site Caddy's message reports not only list all addresses that failed, but typically provide the reason why the send failed - such as a non-existant account. You can use this information to not only update your Site Caddy member account, but also your main database of member data.
Good way to keep contact database up to date.