Blending usually adds complexity and depth. But it should be clear on the label that the wine is a blend, and thus a varietal should contain 100% of that variety. White wines can benefit from blending as much as reds. Blends of crisp, edgy Sauvignon Blanc and luscious Semillon are the norm in white Bordeaux wines. The wonderful white Rhône blends incorporating aromatic Viognier, herbaceous Roussanne, or creamy-textured Marsanne are a case in point.