OK.
If I note that: “Since Defining an OSC value has no effect on PULSIN. The resolution always changes with the actual oscillator speed.”

What then is the true usefulness of this DEFINE OSC command?

Simply or imperatively specify in the PBP compiler the actual operating speed depending on a quartz or simply the internal oscillator.

The only configuration of the OSC fuse bits would not be enough?

I would then deduce that this command must always be placed in the program to specify the actual operating speed at PBP. Correct ?