Hello Chris and welcome to the community!
If an application on the computer uses transaction logs to maintain the database consistency, Veeam Endpoint Backup automatically truncates transaction logs upon successful backup.
Note that Veeam Endpoint Service runs under the LocalSystem account. On Microsoft SQL Server 2012, this account does not have necessary permissions to truncate transaction logs. If you want Veeam Endpoint Backup to automatically truncate transaction logs, you need to manually add the LocalSystem account to a group that has the SQL Server System Administrator rights.