Hidding the frame is a bad idea in my opinion.
With all the interface, panels and so on, it is more likely that you viewport isn't using full screen. So if you're about to render a 1920x1080 image you can't "see" exactly the proportion of your scene that'll fit in that canvas.
That's why the aspect frame stands for. It is here to show you the canvas/proportion of the image you are gonna render as it is defined in the "Dimension Preset" parameter you can find under the "Render settings" tab.
If you set this parameter to "Active viewport" the frame disappears because it perfectly fits what you see in the viewport.