I agree it shouldn't be used everywhere.  I use it some labs for longer listings where it makes sense to include it from a file and not put it directly in the latex file.  Another possible use case is when we give them starter code and discuss it in the lab.  In that case, it should already be in a file and could be included in the latex file for discussion rather than having two copies of the code (one in a file and another in the latex file, which could quickly become unsynchronized).  In labs that require more coding across multiple files (ie cython (pyx file and setup.py), or the labs later in Vol3 and Vol4), the file distinction would probably be more meaningful.