BDM is supposed to be an asymmetrical warfare force, not unlike the LSF when it carries out operations deep behind Rheinland lines.
Not only does the BDM gather intel when required, it's meant to disrupt enemy shipping and cause as much damage to the Liberty economy and military materiel as possible while minimizing casualties.
Another facet of the BDM is to sow the seeds of uncertainty into the Libertonian mind - and nothing is more demoralizing than the repeated demonstration of how the BDM can strike anywhere and at any time.