Custom domain support lets you point your own DNS at a tunnel. Add a TXT record for ownership verification, a CNAME for routing, the tunnel service auto-issues a Let's Encrypt cert, and traffic to app.acme.com flows to your localhost.
When it matters: production-like dev URLs (some auth providers gate features on the domain), branded staging environments, public demos that don't reveal the tunnel service's name.
lrok includes custom domains on the Pro plan. The DNS verification flow is two records and ~90 seconds of cert issuance.