Performance implications of unused vertices

What are the performance implications of unused vertices on a mesh? I have some procedural meshes that can scale in detail. I can precalculate the level of detail up to the vertex limit (65000) and preload this into the mesh (so its stored in graphics memory?). Then use a small percentage (like 1-5% in normal use cases) for triangles but update the triangle list only when increase LOD. Would this be more performant than putting in just the vertices I need and updating both vertex and triangle list?