Pros (?): The Germans got a lot of free labour out of it, freeing up men for the front. Even Oscar Shindler had kids polishing artillery shells.
All the "undesirables" were taken out of society, fear that you too might disappear into the camps kept people in line and working hard.
No unionists, agitators, Communists or "peaceniks" to slow things down, give a different opinion or disrupt the war machine in any way.