Volumetric lighting is accessed per light just like lens flares.  Through use of Lightwave's preview system, called VIPER, you can adjust the light easily relative to the rest of the scene without extensive re rendering.  Just render the scene and that render is then stored in VIPER.  You make changes to your lights settings and a quick preview is made in the viper window.  Of course you will not see the full results until you do a complete new render but VIPER will save you an awful lot of playing around with effects once you get used to using it.