The pars service is present to allow you to maintain the docroot álà java-style/CLASSPATH, sorta. It allows you to store items that would normally be required to be in the docroot, in special archive files called par files. So instead of just looking in the docroot for docroot items, it first looks in the par files specified in th parFiles configuration variable and only then, if parFallthrough is specified, look in the docroot.