Why is guest resolution higher than the native resolution on retina

On MacBook Pro 13, the native resolution is 2560x1600. However in parallels Windows resolution is set to 3360x2100. Why is that? Doesn't it cause a performance issue because of painting unneccessary high number of pixels?

In full screen, I set the resulution to 2560x1600.. I find the text sharper, more consistent at this resolution. But in other modes, for intance in coherence, Parallels forces it to 3360x2100.. Is there a way to set it to native in those modes as well?

 

Hi, please check this KB for resolution settings - please try another resolution in virtual machine settings (Scaled/Best for external displays)

 

Hi, I already read that.. My question is whether there is a way to set it to native resolution in coherence mode.. The full screen mode of MacOS makes task switching too slow with its unneccessary, jittery animation.. In windowed mode the native resolution causes smaller window.. I really do not understand why Parallels forces this, instead of drawing onto a smaller background bitmap and drawing it on to the display..