Go into dsr and select thr res/resolutions you want. Then in the game, set your screen res to 4k for example. Also, I would lower the smoothing option to around 10 if you're down sampling from 4k.
In BF4 I noticed a difference, it's not huge, but every little graphical improvement is welcome. I mean nothing can replace high native res, but dsr seems to help visual quality a tad bit.