While it might be sufficient for most use cases to have the Parameter Number of a MIDI CC set to the CC number itself, there are use cases where a separation of the two values would be beneficial.
Example:
The Clavia Nord Lead/Rack 1 allows direct control of most parameters only via MIDI CC. For its multi-timbral sound engine, there are four different sound slots. The parameters of the four slots are controllable via the same MIDI CCs on different MIDI channels (e.g. Filter Cutoff is CC 74 for all four slots, just on a different MIDI channel).
Unfortunately, some parameters of the Nord Lead, in particular all Shift functions are accessible only as part of a complete Sysex patch dump. Since this complete patch is rather large, it wouldn’t make sense to use it when not absolutely necessary. In order to perform a correct patch update for these special parameters, one would need to create a Sysex message that is referencing also all MIDI CC based parameters. Of course, that would require addressing them all individually, thus needing a separation of Parameter Number and MIDI CC.
As a solution I would imagine two dedicated fields, one for the Parameter Number one for the MIDI CC. By default, they could be set to the same value and thus behaving like the current implementation. But it would allow making a MIDI CC referenceable via a number different than the CC for special use cases like the one explained above.
Hope that makes sense! And thanks for making this awesome device!