Every Jpeg file>save or file>save as discards data
Every Jpeg file>save or file>save as discards data
I don't really concern myself with RAW vs. Jpeg in editing. What I DO concern myself with is the amount of data discarded from the file on any and all Jpeg functions which involve the creation of a new file, including the first Jpeg out of the camera.
Jpeg is a lossey algorithm that discards data from the file on every edit>file>save or save as. This should be obvious from the choices one makes on quality out of the camera, as in fine or high quality vs. standard or low quality on Jpeg creation. It should also be obvious when one gets that last dialogue box, in most editing software, on saving a Jpeg, where one chooses the % quality of the image.
You are instructing the camera, or the computer, specifically how much "like" data to round up and throw out of the image.
I believe more people would shoot RAW + Jpeg if they realized how a Jpeg degrades EACH time it is saved once at creation by the camera and each time you edit/change the image.
It only takes about 8-10 saves in the computer using a low percentage of file save in that final dialogue box pertaining to Jpeg quality, to visually detect degradation.
Jpeg stands for Joint Photographer Experts Group, the people who got together long before we had "broad band" over the internet, to devise a compression algorithm for files that would speed transfer via telephone modems and similar problems.
With the advent of broad band internet and cheap storage, Jpeg may actually be somewhat obsolete considering it's originally intended purpose, but the camera manufacturers will surely not let it go. Too heady to explain to the end user/consumer.
And, for some people, the processing engine in the camera takes care of a lot of hours of begrudged time spent in front of the computer. So, in that case, the first Jpeg OOC is useful and a great time saver. If you take the time to properly understand your computer and it's internal "edit" functions, Jpeg gives you the opportunity to get very satisfactory results bypassing a lot of time spent massaging raw.
So the point that makes the most impact for me is the fact that EVERY Jpeg loses data on the save, because the file on a save is a new file and the Jpeg function ALWAYS discards SOME or much data depending on your choices.
If you never intend to edit (using ANY software that offers a Jpeg save) you pictures, then perhaps that one first Jpeg save OOC, is perfect for your needs and has enough data for a high quality image, using High, Fine or Super quality. That way the data loss is one time only, OOC, and minimal loss because of the quality selection, in addition to the resolution (pixel count).
So I can agree with Nick and everyone else on this thread, as long as you understand the degrading impact that Jpeg has on repetitive editing and saving of the file.
Some people also believe that opening and closing or transferring Jpeg files runs the compression algorithm and that is NOT the case.
This is a very helpful article on some of the Jpeg myths:
http://graphicssoft.about.com/od/formatsjpeg/a/jpegmythsfacts.htm