With DNGs I like the jpeg previews so I don’t have to open Lightroom to view them.
What software do you use for previewing your RAW files? Most software should be able to preview NEF just as easily as DNG. (I use FastStone Image Viewer which works great for all types of RAW files.)
I also like DNGs because if I ever didn’t have Lightroom I could still open the pictures in my older editing program.
What is your older editing program? 🙂 The more info we have, the better we can advise you! If you’re talking about simply viewing your RAW files, then you don’t need to worry; there is plenty of software that can view NEF files.
If you are worried about losing your LR edits, then set Lightroom to save sidecar XMP files with your edit info beside each file. That way if you lose your catalog to corruption or HDD failure, (or if you quit paying Adobe for a subscription) you’ll still have your edit settings archived with the original RAWs. (That’s assuming of course that you back up your originals offline from your main computer drive. HIGHLY RECOMMENDED!!)
If you like processing a lot of technical info, here’s a thread on the topic from DPR: https://www.dpreview.com/forums/thread/3336786 If you don’t have time or inclination to process all of that, I’ll give you the gist of it here. 🙂 Basically, there’s no real advantage to converting your NEF files to DNG. You do not gain any “quality” by doing so; in fact you lose certain Nikon-specific metadata info in the conversion process. DNG is purported to be a “universal” file format that will be “future proof” but the fact is that hundreds of thousands of photographers shoot NEF files with their Nikon cameras; that file format is not going to go anywhere for a long time. And if for some reason it does, you can then batch convert your whole library at once if you feel that it’s necessary.