Consider the fillet in the soap dish model. If the top surface were undersized for some reason, or the fillet radius didn’t reach to the top surface, an extend operation could resolve the problem. In this case, select the Extend surface option from the Surface toolbar.
Unless you’re sure of your process, it’s safer to create a new surface instead of modify an existing surface. Set the Create new surface radio button and name it. Working through column and row options and previewing the results, the intended surface is achieved using First Column and an extension of 0.1 inch.