Using shell commands versus C equivalents

[Garrett Cooper]

Another simple question (I hope):
    Is there any reason why shell commands should be used in place of a 
C command (in this case chmod via vsystem instead of the chmod(2) 
function)? It seems like the fork / exec would be more expensive with 
the shell command, but any area where code could be optimized is more 
than welcome I would think.
Thanks,
-Garrett