When applying multiple textures to a mesh, like for bump-mapping, I usually bind the textures to the first few fixed texture units, e.g.: diffuse = unit 0, bump = unit 1, specular = unit 2, then keep reusing those to each different mesh with different textures. But I've always wondered why
glActiveTexture supports so many texture units (in the previous link, it says at least 80).
So it occurred to me that one possible way of managing textures is to bind distinct textures to each available unit and leave them enabled, just updating the uniform sampler index. That should improve rendering perf by reducing the number of textures switches. If you have less textures than the max texture units, you never have to unbind a texture.
Is this standard practice on real-time OpenGL applications (I believe this also applies to D3D)? And are there any non obvious performance implications of taking this approach? Memory overhead perhaps?