Hi Amateur,
The advantages of Companion are that it gives players a centralized place from which they can view and “manage” all their Grand Privé accounts. The player can keep their details up to date, view the transactions that have occurred on the account, check up on the balances (both cash & bonus) in their accounts and, as Daera mentions, they are also able to combine loyalty points and to redeem them across accounts (e.g. you can redeem CGB points for bonus cash in your LP account). Additionally, they will also receive special promotions (should they qualify) that they might not otherwise receive.
For more information, please visit: http://www.grandprive.com/companion
Regards,
Yashin