In many cases a company using Azure AD B2C wants to customize the user flow's UI e.g. prefill some fields or hide certain sections or pages (e.g. when doing signup via phone it is not necessary to ask a user to fill the country code if the product is built only for Australia).
It is currently possible to customize the B2C user flow's HTML page manually only. While this is a viable option, the automation is much preferred, especially for a company having multiple tenants and environments. Although the Graph API allows creation of B2C user flows programmatically, it currently defines no way to set the "Custom Page URI". It would be very useful to add the "Custom page URI" property to the b2cIdentityUserFlow resource so that a user flow with a Custom UI could be programmatically created.