However, results for individual codes may vary. Generally this value is only used at runtime. On the other hand, it often works regardless of the setting. Small codes may get all processors requested, but it is highly unlikely that a large job will acquire all 12. Alas, with this ease comes hidden costs.
Some codes actually run slower, even in wallclock time, on more processors.
Also, increasing the number of processors will not speed up unparallelizeable sections of code. You can see how effectively the code is parallelized by including 'ja' in your submission script. Here's an example including setting the environment variables. In codes that are not parallelized well, the majority of time would be listed as connected to only 1 processor. However, the usual reality is a pandemonium, where when the master processor attempts to assign tasks far fewer than the full amount of processors requested are actually available.