Just discovered this add on a few weeks ago. It allows you to run formulas on data from rows after the information is entered into the spread sheet from Google Forms. This was not possible before as any new information from the form was put into a row that had nothing in it already (meaning you couldn't have a formula there ready to run). copyDown makes this possible though.
I discovered this while creating an online practice chart that students can fill out and submit via the web. Once I have finished that project I will be publishing a video tutorial so check back later!