The render quality is used for incrase or decrase the preformance and quality it can be good for low-end computers and 4k screens high levels are as antialiasing for example.

Is this for anti-alisting or for another feature?

Yes, that is
is like an option for have better perfomance without have lower resolutions test it in Optifine for example

I think he means decreasing the render-resolution without changing the global screen resolution, so that 1) one can tradeoff image sharpness for the game rendering for higher FPS, while 2) maintaining super-crisp rendering of UI elements (which are still rendered at screen resolution.

The anti-aliasing can be achieved by doing render-resolution larger than screen resolution, but that's not as much a compelling case, given that many shaders have their own TAA/FXAA integrated.

Merging into #757, which contains more information.