Either can be used, depending on your workflow.  Live re-renders allow for realtime monitoring and recording directly to the DAW vs offline exports and importing to your DAW.  of them via Dolby Renderer Return plug-ins in Pro Tools, Offline re-renders can be exported faster than realtime direct to disk.   While each offline re-render is created faster than realtime ones, depending on how many re-renders you are creating and your overall CPU load will determine which process is quicker, as you can generate up to 10 re-renders in realtime using the live re-renders.   

Live re-renders can be recorded back into your DAW using the audio output device set in the Renderer Preferences (MAC) or Settings (Windows), Driver tab.    Live re-renders can also be recording back into Pro Tools using the Renderer Return plugins if using the Dolby Atmos Production Suite.   Live re-renders can be recorded into a DAW using the Dolby Audio Bridge but only when playing back an open Master File.   You cannot use the Dolby Audio Bridge as the Renderer input and output device simultaneously to record live re-renders back into your DAW with the Renderer source set to input.