I purge my carboys with CO2 before transferring (if I'm using a secondary). I like the results. If your bottling though, I'm not sure I'd purge my bottles. I've always been under the impression that the yeasties use the head space Oxygen to carbonate the brew. Although, I'd assume there would be enough residual in the beer to accomplish that. Anyway, for the carboys it definitely couldn't' hurt.