I was convinced fairly early on to convert to DNG on import mainly for backward compatibility with software, should I ever find the need. The one drawback I found was that a site that post photo challenges require winning entries to be verified with the original RAW file to check dates and make sure no illegal edits were performed, and they do not accept DNG files as it "changes" the original RAW file. This rendered my entire back catalog unusable in contests that allow you to go back. The site is a PITA and I've since left in disgust over some of the nonsense there, but if stuff like this is important to you then at least back up the NEF files to an external drive after conversion so you have them.