In labour camps, most inmates were used for slave labour. 
  There was a policy of death through work. Even though this work 
  may have been useful for the German war effort, their lives were expendable 
  as far as the Nazis were concerned. When they could no longer perform useful 
  work, they would be taken to the gas chambers after one of the many selections 
  that took place.
  
  As well as the maintenance work, road building and quarrying that the prisoners 
  were made to do for the SS, many large German companies made use of their labour. 
  Frequently the inmates were marched out of the camps, through towns to private 
  factories. Some of the industries were vast, such as the multimillion pound 
  consortium IG Farben, which established a rubber works near Auschwitz.