Converted Library to DNG now what about those other files?

Question

I've just taken the plunge and converted all my CR2 images to DNG, replacing the originals.
However, I still have all the JPEG sidecar files left over. Can I safely delete these, or are they required by the DNG?
Also, I was previously using the option to write to XMP sidecar files. With DNG is there any real need to keep doing this?
Thanks

Answer 1

Converting RAW files to DNG does not replace the original file. Rather it places all the data from that file inside the DNG in a standard published format. It can also contain a full copy of the file in its original format if you select that option (although this is really a waste of space). Think of DNG's as a box with a standardised filing system into which you file your data previously filed in a way only understandable by Canon, Nikon or whichever company designed the format. DNG's have a filing system that allows anyone to now read that data instead of just a few people "in the know".
The DNG files will allow you to write what was formally contained in the sidecar files directly into the headers of the DNG file. If you had  automatically write all changes into xmp selected in catalog settings, then this will continue with DNG files but now write the data into the file header rather than as a  sidecar file. If you wrote the information yourself (by selecting write metadata to file from the metadata tab), rather than doing it automatically, then you can continue to do so. If you don't select this changes are stored only in the LR catalog and not in the file itself. The advantage of writing data into the file header (or as a sidcar file) is that other applications such as Bridge can read this data and if you import the DNG into a different LR catalog you can read the changes into that catalog, by selecting read metadata from file. The disadvantages include a small performance hit particularly on less powerful systems, you can still write the data to file manually in this case.
As far as jpg files go, if these have been imported as separate files and you still want to keep them as separate files then don't delete them. To ensure any changes you make in LR are written into the header files then select this option for jpgs, Tiffs and PSD files in catalog settings on the same screen as where you set the options for xmp data for RAW files.
Jpg files are not required by DNG's that contain a RAW file. A jpg preview file is embedded inside the RAW file and this will be also in the DNG file and used by applications not capable of decoding RAW data.