somebody already mentioned permissions, but you may also want to specifically set your umask inside your script, depending upon how any output files are being used...

I once wrote a cron job that did a little auto-emailing of some aggregated numbers (from a flat file) overnight to users throughout our company...well, since I didn't set my umask, the permissions on files I had been updating overnight were set so that no one else could write to the files. Kinda freaked our users out ;)