Depends on the bike. On the XS650, the clamps bolt onto the triple tree with big rubber bushings. When you remove the assembly, all that's left is a big round hole where each clamp used to be, right next to the holes for the forks. Looks decent - no grinding necessary.
On the BMW, same sort of deal - clamps bolt down to the triple tree and when removed just leave two 6mm holes.
On Hondas etc. where the bottom 1/2 of the clamp is cast into the tree, as Crash has pointed out many people make up a simple rectangular plate to cover the area up and use it to house switches/lights etc.