Any emulator running at 1x resolution on the Switch has zero issues with the GPU. It's always been the CPU holding things back and this changes nothing there.
The only time this would make a performance difference is if you dialed back the resolution on a 3D core. Like say, maybe you want to run Flycast handheld at 1x instead of 2x, maybe this would help cover the lower resolution sins a little. FSR is not great at bridging huge resolution gaps so I would not try to upscale your 240p games and the like with it, there are better shaders for that.
The only time this would make a performance difference is if you dialed back the resolution on a 3D core. Like say, maybe you want to run Flycast handheld at 1x instead of 2x, maybe this would help cover the lower resolution sins a little. FSR is not great at bridging huge resolution gaps so I would not try to upscale your 240p games and the like with it, there are better shaders for that.