AA Makes jaggy edges smooth. It uses VRAM but you dont really ned it at higher resolutions, as when the resolution is higher, more pixels are used so it automatically takes the jagggies away. I cannot live without AA. There are different types of AA, such as super/multi sampling, temporal AA and stuff like that. Im not too sure , but i think that temporal AA actually adds pixels to make thin objects (such as a metal bar in a gate for example) look smoother.
AF just makes textures in the distance look less muddy. I dont really notice the difference between when it is on and off, so i just keep it off all the time.
4x AF is generally performance hit free. AA Takes much more of a FPS hit than AF in general.
Hope this helped ^^