For debugging purposes only, I do log the contents of the sidebar (users and shift definitions) so that I can help troubleshoot when users have difficulty with the spreadsheet, and to help find bugs. I only log this information in the standard Google Add On logging software (Stackdriver logging), which periodically deletes its older logs. I do not store this information anywhere more permanent such as another spreadsheet, and I promise to use it only to help resolve technical issues and resolve bugs.
I do not log any of the specific details of your schedule that are stored in your spreadsheet such as when your users are working specific shifts. I cannot view your spreadsheets or google calendars as they are created by Shift Scheduler.
It should go without saying that I will never share or sell any of your information for any reason, but I'll say it anyway: I will never share or sell any of your information for any reason.