Though clearing the render meshes makes the file smaller, it will shade and render more slowly the next time you open the file. Exports a rectangle that corresponds to the current viewport boundary. It is useful for registering curves to renderings or screen captures taken in the same view. Before exporting, position the objects in the active viewport the way you want them to fit the page in the illustration program. Curves have fewer control points than the original because the Adobe Illustrator file format only supports non-rational cubic Bézier curves. Rational curves or curves higher than degree 3 are approximated with a cubic Bézier. If you draw curves using the free-form curve tools degree 3 or lower and export them from the top view, they won’t get refit and will look exactly the same in Adobe Illustrator. Source.