All camera makers use proprietary RAW formats, That's why Adobe tried (and continues to try) to get everyone to use DNG, so that there is a single cross platform format
If you give a client a RAW image, he or she won't be able to see the edits you have performed of the image, unless you also include the XMP file for the RAW image. But if you save the image to DNG format, then the client can see the edits. The worst thing would be to have only DNG as the universal format.
Also, lets say one or more camera manufacturer abandons its RAW format for something else; in this case DNG can still be used to open and edit the abandoned RAW format. Another good thing about DNG is that the file is smaller that the RAW image, and also that the photo's metadata is embedded in the DNG file (you don't need the XMP file).
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