It's safe.
If you have a monitor that is 1920x1080 then you are still sending it a 1920x1080 signal, you just process at a higher resolution first then DOWNSCALE that after similar to current methods that upscale and downscale to perform anti-aliasing.
So the monitor is getting a normal signal, and the GPU doesn't care as it's just crunching numbers like it always does.
Whether you SHOULD use it depends on a few factors so you should experiment with the chosen resolution and smoothing. There's an ideal combination that lets you hit your target frame rate but that varies by the game.