Whether you are wearing a suit and tie or a pair of jeans and a sweater, your dressy shoes should not have a rubber sole unless you are taking the Virginia bar exam. After you find out that you passed, you should give those shoes to Goodwill.
A leather sole has many benefits. It is less casual. It gives your footfall a distinct but unobtrusive sound (the very reason which the Virginia Board of Bar Examiners forbids them on the unforgiving concrete floors of the dark, yet bright, Roanoke Convention Center). It makes for a leaner shoe silhouette (though leanness is a matter of taste; mine skews toward the slender and pointed).
A leather sole lasts longer. It tends to be attached to a nicer leather. It makes re-soling easier so that you can make a beloved pair of shoes last for decades (generations, if they're made of cordovan, a type of leather made from horsehide and which tends to have a very rich burgundy color and lasts forever).
Finally, when you cross your leg, the sole looks careworn yet classy. This is especially important when you're wearing sharp jeans. Wouldn't want to accidentally dress them down with a clunky, dusty rubber sole.