A custom domain is a way to create links that include your brand, i.e. replacing “neon.ly” or “neon.page” with something of your choice.
When a link includes your brand, people will associate your links with you or your company. Seeing your brand, they also trust your links, resulting in more efficient click-through rates.
For example, when Wengler shortens a link with neon.ly, instead of being branded as neon.ly/3th3Rr the link shows their own custom domain (wnglr.lu/3th3Rr).