In Herbert's fiction, sometime in the far future, government has become terrifyingly efficient. Red tape no longer exists: laws are conceived of, passed, funded, and executed within hours, rather than months. The bureaucratic machinery has become a juggernaut, rolling over human concerns and welfare with terrible speed, jerking the universe of sentients one way, then another, threatening to destroy everything in a fit of spastic reactions. In short, the speed of government has gone beyond sentient control (in this fictional universe, many alien species co-exist, with a common definition of sentience marking their status as equals).
BuSab begins as a terrorist organization, whose sole purpose is to frustrate the workings of government and to damage the incredible level of efficient order in the universe in order to give sentients a chance to reflect upon changes and deal with them. Having saved sentiency from its government, BuSab is officially recognized as a necessary check on the power of government. First a corp, then a bureau, BuSab has legally recognized powers to interfere in the workings of any world, of any species, of any government, answerable only to themselves (though in practice, they are always threatened with dissolution by the governments they watch). They act as a monitor of, and a conscience for, the collective sentiency, watching for signs of anti-sentient behaviour and preserving the essential dignity of individuals.
In the novels mentioned above, Jorg X. McKie is a saboteur extraordinary, effectively the James Bond of BuSab.