Factory resetting the devices is not mandatory. However, if it is not performed, the client will only have access to a version of the MDM with limited controls — without all the Policy features, which are exclusively available in the AFW version. Therefore, we strongly recommend performing a factory reset.
This requirement is a prerequisite from Google itself for using Android Enterprise. All MDM tools that utilize this management model must follow the same procedure.
For cases where data cannot be lost, it is recommended to back up contacts to the device’s Google account. After the factory reset and during the enrollment process, the same account should be added to the device to restore the data.