The interests of nation states should take predecence over the normal legal procedures in certain cases, not all of which can be foreseen in advance or codified. Therefore it is necessary to have a blanket legal exemption from standard operating procedure which can be invoked in certain cases when needs must.
The concept is often only loosely defined, if at all. It is often associated with censorship of information. Another application is the non-prosecution of people who would normally be subject to legal proceedings. In both of these cases, it can be hard or impossible to know whether any such compelling interest actually exists, or whether it is being used for selfish means by corrupt officials.
The concept is outdated and doesn't fit with the 21st century world in which a supranational deep state controls multiple governments.