MDM is designed for corporate owned phone environments where there's a great many good reasons to lock down a phone. If you're handing out company owned phones to employees you want the ability to remotely lock/wipe, install and remove apps, set a number of restrictions. If people want to do anything else they are completely welcome to do it on their own personally owned property.

For instance I have recently seen a very successful Apple MDM deployment in a school environment where the teachers and staff have access to a great depth and breadth of PII of a thousand children under age 16. You don't want all those phones to become a free-for-all of people doing whatever they want.