They were created for the efficient killing of Jews and undesirables.
First the Germans tried mass shootings. This was difficult for body disposal, and the toll it took on victims and executioners alike slowed operations down.
Then they tried mobile gas vans, where victims were herded into trucks and suffocated with gas fumes. This too proved inefficient and time-consuming.
The next step, the extermination camps, made the whole process compact and efficient - bring in thousands of victims by train, strip them of their valuables, gas them in huge chambers and then burn the bodies in ovens specifically designed for that purpose.
That beautiful Teutonic efficiency was used to commit mass murder on an assembly line basis.