Hi Arun,
In general. Control Key is the Mandatory field, which needs to be maintained during Routing creation.
If it is maintained at the Work Center level, the same will get copied, once assigned, if required, Control Key can be changed in the Routing Operation level, during the creation.

Hope, this is clear. Please let me know, for any other details required.Thanks & Regards : Raja

Dear sir.

This is right but its not my answer.

my question is this what impact on production cycle without control key.