For the brand.
For phishing attacking prevention.
It is better for the brand and it gives some level of prevention against phishing attack on the domain name. Because scammers must have skills to create a vanity onion address.
It doesn't prevent phishing attacks though. Popular bitcoin mixers have had scammers go after cloning their onion links as well. Just check this thread and you will see a number of reported copycat onion links
1.
https://bitcointalk.org/index.php?topic=5381839