Ahh, if you wish to delete them also, you will need to run a separate perl script
Here's the topline comment from that script to give you an idea of what you're looking at...
#!/usr/bin/perl
#
# AST_CRON_purge_recordings.pl version 2.0.5
#
# IMPORTANT!!! used to delete recordings!!!
#
# runs every day, goes through recordings older than a certain number of days
# and deletes those recordings that are not of a certain status
# default is 30 days old to remove non-sales
#
# put an entry into the cron of of your asterisk machine to run this script
# every day or however often you desire
#
# This program assumes that recordings are saved as .wav
# should be easy to change this code if you use .gsm instead
#
# Copyright (C) 2008 Matt Florell <vicidial@gmail.com> LICENSE: AGPLv2
#
#
# 70917-1339 - first build
#
As far as what's safe to delete - the biggest culprit will be your /var/spool/asterisk/monitorDONE/ORIG directory. These are all the uncompressed WAV files after they have been processed (not necessarily FTPed yet). Assuming you have your archive script set to FTP all your MP3s only, you can safely delete the contents of this directory after each night if you so desire.
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Cluster Installation, ViciBox Server
VERSION: 2.6-372a
BUILD: 120713-2123