Spam filters and recipient servers look at the links within emails to determine whether the email looks trustworthy enough to deliver - they use the reputation of the root domain to determine whether the links can be trusted. Implementing link labeling helps in email deliverability because you are no longer relying on click tracking going through a domain that you do not control.
In an attempt to clarify complex functionality, SendGrid is upgrading the name of Whitelabel. A whitelabel is now generally called sender authentication. A domain whitelabel is now called domain authentication. A link whitelabel is now called link branding. An IP Whitelabel is now called reverse DNS.