[Csnd-dev] nchnls_hw question

working on an example for this opcode, and thus trying to understand and
apply this, i am unsure what the output of nchnls_hw represents.
In the manual On init-pass idacc will contain the number of channels in the
output device, and iadcc, the number of input channels.
My output for both idacc and iadcc is 32. I can not attach a screenshot
from my Jack system in this list, but i have a lot less audio in and
outputs. What does this opcode reveal, other than the for me useful in and
outputs? What is 'hidden' for the user?