This table gets EXTREMELY large in row size.
When performing certain clean up tasks by going to Utilities -> System -> System Cleanup we have tools that can clean up the following:
FileSystem - Prune Old Attachments
FileSystem - Empty Template Cache
tblactivitylog - Prune Client Activity Logs
tblemails - Prune Saved Emails
tblgatewaylog - Empty Gateway Log
tblticketmaillog - Empty Ticket Mail Import Log
tblwhoislog - Empty WHOIS Lookup Log
but there is nothing for the tbllog_register table. On a clean install of WHMCS, the table already starts out at +-2300 records and over time this grows immensely. My own table is sitting on 206 782 rows as we speak and it's clear that this table needs to be included in the list of cleanup tools as it can hinder restores when it needs to insert hundreds of thousands of rows. having a large table can also reduce performance and thus we should have the abilitiy to clean it up.