I used to own an HK AVR435 that had this capability. It seemed a bit odd to me, but here's the explaination from their manual:
When any needed adjustments are made to the crossovers, one additional adjustment is available to custom tailor the way information is sent to the subwoofer.
The LFE LP FLT line adjusts the frequency cutoff of the low pass filter that determines the frequency at which information is sent to the subwoofer when playing a digital soundtrack that has a dedicated low frequency effects channel. In most cases the default frequency of 120Hz is appropriate, since that is the frequency most commonly used in the creation of LFE channels during a movie’s sound mixing process. However, you may wish to change the setting based on your individual preference or the characteristics and capabilities of your subwoofer.