Constant current is a very useful feature of today’s controls. If this feature is present and you ask for 10,000 amps. The control will deliver that amperage each weld. It won’t matter if you are near the edge of the part or putting half of the file cabinet into the throat of the AC machine as you move across the part. The control with constant current will deliver 10,000 amps to the weld. It has a feedback coil that tells it the amperage that is flowing and it makes corrections to deliver the proper amount during the weld.
This is a great tool for AC welding where magnetic material in the throat will change the current flow. Another case is as the machine shunt wears the constant current control will insure the proper current reaches the part until the proper maintenance is performed on the shunt.
References: RWMA - Resistance Welding Manual 4th Edition