I use 14 bit instead of 12 because it should give better shadow detail.
Lossless compressed does not alter the NEF data, it just stores it more efficiently (just like a ZIP file). I do not use compressed because it throws away some of the raw data to get greater compression. The decompressed data will be different than what was originally recorded in the camera.
Decompression probably adds a bit of CPU time when opening the file, but that time is not noticeable. Transferring the compressed files from memory card to computer disk will be a quicker because of the reduced size. Obviously the compressed files take less storage.
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