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Guys,
you have to be aware that the purpose of INCR is not to reduce the noise, it is here to deal with hot pixels only.
What INCR actually does, it subtracts one dark frame from light frame.. This removes hot pixels from the frame, but at the same time doubles the noise power (because, noise being a random signal, it cannot be removed by subtraction - subtraction is the same thing as addition from the noise point of view).
This means that to arrive to the same S/N ratio in the final image, you have to stack a greater number of subframes, to average out the noise.
Practicality is another issue, and sometimes INCR is beneficial (when exposures are short and numerous)
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