the concrete example is a library that has a CS pin, a ENABLE pin and an INT.
Sometimes it is not necessary to use them, because the program does not require it, and it leaves me pins that I can not use. I thought that a none would put a -1, and so could avoid losing a pin.
Here is another example, the EN pin sometimes does not need to be used, but it removes an arduino pin.
ps: In an arduino library I saw that it uses -1 to not define that pin and thus leave it free for another use.
If instead of using input-port I use input-number I solve the problem. But I found that NONE = -1 better in input-port, I do not know if it would be possible