Agency Plan operators frequently run multiple businesses or product lines that each warrant their own booking subdomain. Currently the single custom domain limit forces a choice: which business gets the branded subdomain, and which uses the default tidycal.com/username/... URL.
Real example: an Agency Plan user running personal consulting at schedule.firstname-lastname.com and a separate productized service that ideally lives at booking.companyname.com. Both businesses pay the same Agency Plan; both deserve branded booking URLs.
Suggested implementation: allow up to 3-5 custom domains per Agency Plan account, with each domain mappable to specific booking types or used as the default. This keeps the Agency tier meaningfully differentiated from Individual and gives multi-business operators a real reason to upgrade and stay.