  Consciousness is useful when sickness increases in the body. As the malady rises to the level of consciousness where the self becomes aware that there is something wrong, internally, with the body, higher level cognitive thought comes into play in order execute procedures to alleviate the sickness. That is, instead of continuing to roam about looking for food, shelter, and sex, these "normal" everyday behaviours are overridden by consciousness to enact different, sickness-prevention behaviour, in order to ensure the survival of illness as a new priority. If we were not aware of such ensuing illness, and continued with our normal routines, perhaps the sickness would kill us. Even worse, we would spread said illness to the rest of the group, diminishing the survival of the species as a whole. Consciousness can thus be very useful. 
