The main benefit of the Front end transport service is to reduce the direct load on the Exchange Mailbox Server which holds the main transport service 

Since the Mailbox role is the core component from Exchange 2013 and it does most of the job and not only the message categorization and routing Microsoft introduced the front end transport service for authentication and proxying the connections 

What is/are the benefit(s) of having the front end transport service to proxy SMTP to the MBX servers over and above sending mail directly to a M