Sometimes the same container type can be used for input or output purposes. For example, a STATE_TYPE container (which is a basic True/False state) can be used for a button (read-only) or a relay (write-only). This is no big deal regarding the capability of your code because you deal with the messages as you want and make it work as you want, but other containers don't know if it's read-only or write-only.
This new access management feature allows you to declare the readability of your container for the other containers in your device. By default, a container is on a READ_WRITE_ACCESS, and you can choose to make it READ_ONLY_ACCESS, WRITE_ONLY_ACCESS, or even NO_ACCESS.