What is LBA?

What is the purpose of the LBA? And I've seen many patches (www.xeal.cjb.net) that let you change the LBA of the second session from 11700 to 11702. But for what??? Will the game boot better if I change the LBA?
Another question: I have use cdirip to extract Tdisc.cue TAudio01.raw and TData02.iso from a cdi image, so that I can apply a patch on it (the game is Jet Grind Radio). Now my question: How do I convert the extracted files back to a cdi image (or Nero)?