I’ve come across this utility before - using it seems to add input latency according to the reviews it has on Steam. So using it to increase performance isn’t really better than not using it, it’s just a tradeoff.
If you’re not sensitive to input latency then that’s likely going to be a good tradeoff for you, but if you are (or play competitively) it’s not.
That’s one of the program’s common usages, yeah. Among other things (like integer scaling for pixel-based games), it can be used to render a game at a lower “internal” resolution and then apply one of several upscaling options to make up the difference, improving performance and hence “free FPS”.