I cycle all my new packs once before running them on a car for the first time. But I do not do this to break them in. There is no reason to break packs in.
I perform this task for 2 reasons:
-The main reason is because I want to see what the numbers on the newly assembled pack are. I am not looking to test and see if the matchers numbers are true, but I am looking for reference points or numbers of when the battery is new so I can compare it to the numbers as the pack ages.
-Nimh batteries, when they have sat for long periods of time can become flat and sometimes need a cycle of 2 before their performance is restored. The high majority of my packs are freshly matched so this is not a main concern of mine anymore, but I beleive this is a good practice if your batteries have been in storage for several months or more.
But to be honest, I probably would not cycle my batteries when new if not for the fact that I get new batteries all the time. My oldest batteries have at the most 9-10 cycles on them and then they are replaced. Batteries only have a finite amount of cycles they can be put through before they start degrade in performance. Cycling the pack when new is one less cycle of the pack that you will be able to run in the car.