Azure AD P1 and Autopilot question

Hi VK

1) The AAD licenses would be assigned to users, not devices. Licenses can be reassigned, but you would need to ensure that users aren't leveraging any other capabilities of AADP P1 prior to the licenses being revoked and then losing those features as well.
2) The biggest initial benefit you get by adding AADP P1 to Autopilot is that the devices will automatically enroll with Intune after performing the AAD Join, rather than it being an extra manual step. This means that if a device reset is performed, and the AAD P1 license isn't assigned to the user, the device will be AAD Joined, but not Intune managed until that is addressed separately.
3) https://docs.microsoft.com/en-us/azure/active-directory/hybrid/how-to-connect-device-writeback has more details, but two of the main scenarios are WHfB with hybrid certs. and CA via ADFS. Others may have some additional use case scenarios