Reasons for decreasing the number of threads in a parallel implementation

What are the reasons for decreasing the number of threads in a parallel implementation ?

Assume that we have two implementations, the first one with 4 threads, and a second one with 8 threads, and both have exactly the same run time. What are the various reasons to prefer the first one?

I stress on the fact that the two implementations have the same run times.

The obvious reasons are the following:

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If we have 8 processors, we can execute at the same time this implementation on two different sets of inputs thus performing twice the work,

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Less resources consumption by the OS which handles less number of threads.

I'm looking for other reasons...

Some other benefits from a security point of view for running the 4 threads implementation would be :

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Obfuscation of the actual processors being used by the algorithm, in case an attacker is looking to interfere with the execution.

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If you have 8 processors you can run simultaneously the same algorithm twice using the same input to check the integrity of your results.

StackExchange Computer Science Q#16190, answer score: 3