Imagine you have been working hard customizing a graph, changing the
Domain and Range, the number of points and the thickness of the line,
even the colors. And you decide that you have had it, that you just want
the graph to be the way it was before you started. You could redo each
setting, but it is quicker to click Customize and then Restore Defaults.
Everything will be back to the way it started
If you have done all you want with one graph, and want to start afresh,
click 
to remove all your curves.