They're basically beat cops with a somewhat extended capacity to patrol. Their role is primarily deterrence and community relations. You put these guys where you want a visible police presence. The cars are for rapid response. I mostly see bike cops in downtown areas or other business districts.
Not sure what you mean exactly by "addressing crime". Outside of pulling people over for speeding, most times I see any police officers who ride in cars, they're just driving around. I generally try not to be at an active crime scene.