Native 4K support is always better than Dynamic Super Resolution (as Nvidia calls it, not sure of others) especially these days that now 4K monitors got cheaper and well optimized. Just make sure the monitor has good specs like low input lag.
Higher DSR gives effects similar to anti-aliasing on lower resolution monitors that is held back by the native resolution output due to rendering in 4K then zoom it down to the lower resolution of the monitor. It is like opening movie then resize down the video player from the edge of the window with the mouse pointer. It could look weird.
It is still nice, but later on when filtering can be used on 4K without too much performance loss, true 4K monitors can go even higher in image quality. Also since DSR is synthetic, it might not always run as desired on different settings and apps like games and desktop.
Performance wise, DSR 4K and native 4K both have the same performance impact.
I never use virtual super resolution or whatever. They put a bigger load on your components and everything looks weird, like out of proportion. Also, I'm not sure how it can benefit your experience. I mean, your monitor won't magically get more pixels, it just makes more sense to go for higher AA settings. This all feels like a marketing play and not something that will produce any real impact, other than heating up your card.
I can make use of it. I do it to test my build's capability/performance knowing my TV (I use a smart TV) is max 1080p. Same DSR and native resolutions give the same impact on performance. It also gives a result like AA. In some instances DSR works very well and in those instances one could compare the performance with AA and see which has better performance then pick that one. DSR in Nvidia can have sharpness and blending adjusted. 1440p doesn't work well with me but 4K does, for example.
In some games a lot got screwed up. In others, it worked just as it works on native resolution in terms of compatibility. Dark Souls 3 and Need for Speed Host Pursuit for example work perfectly with me on my setup at DSR 4K. DSR 1440p is blurrier to my taste. I still don't use it for actual game play because I want 60FPS. DSR 4K gives me 25-35FPS and in games like Gears of War 4 it causes some missing high res. textures due to lack of VRAM (only 4GB here).