Between around 2004-2006 I did these consistently, twice a week for 5 sets of 12. I used them with my 4-way split usually on both Bench and Press days. I found them to be a very valuable pulling exercise, for me it had most, if not all of the benefits of a heavy row but without the weak link that is the arms. I worked up to very heavy weights on a cable stack after my chins or rows. I wrote a little about them here.
Nowadays I don't have access to a cable row apparatus and it's just too awkward to try and do this exercise with a bench and barbell so I don't bother. But it certainly has value. A good strong upper back will aid you in pretty much anything to do with powerlifting.