What comes out
The route as one clean line with distance, time and elevation from the file under it, the way the print draws it, at screen size. PNG is pixels at twice screen resolution, for a message or a post. SVG is vectors, for anything that will be scaled or edited later.
Nothing is uploaded
The file is read and drawn in your browser. It is not sent to a server, and nothing remains when you close the tab.
A picture, or a print
An image from this page is right for a screen. For a wall, the same file goes into the editor, which draws it at print resolution for a 30×40, 50×70 or 70×100 cm sheet, one line or on a real map. A screenshot made bigger goes soft; coordinates drawn again do not. Turn a GPX into an image explains the difference, and the tools page has the rest.