It would be useful when using the rotate command during sketch mode to be able to align a sketch to an edge on the plane you are working on. Sometimes the angle of an edge is unknown to the user so it makes it difficult to place a sketch in relation to that edge.
The attached image shows an example where I have attempted to align text to an edge of a model. I know it is possible to project the edge and then align it to the curve but it would be simpler to have a check box in the rotate command box that said "align to edge" and then select the edge.