Several mobile network carriers specify their own LwM2M device management. The LwM2M carrier library facilitates an nRF91 device to connect to the device management servers, regardless of the other actions of the user application.
It is mandatory to include the LwM2M carrier library in any AT&T, T-Mobile, or Verizon certified products.
For the applicable carriers, it is mandatory to include this library in your application for the certification to your end product.
See the Zephyr documentation on Lightweight M2M (LWM2M) if you want to use LwM2M for other purposes.