Primarily to avoid breaking the module. It will also improve your product reliability by preventing system crashes from filling the root filesystem. 

It is a Device Tree Blob. Most desktop Linux machines actively probe for installed hardware to load and initialize various drivers. This can be a slow yet tedious process. To avoid the time required to probe in general, embedded Linux devices use a pre-defined, binary DTB to tell the kernel what is on the board and how to talk to it. 

You need to install the boot-select jumper. Check the appropriate controller hardware manual. 

 You need to set your DTB. 

 You need to set your DTB.