Rapid Verify quickly simulates the motion of the cutter and the removal of material from stock to target. It is essentially a simplified version of SolidVerify that doesn’t support 4-axis or 5-axis milling and some cutters. Most 3-axis users won’t notice the differences between SolidVerify and RapidVerify.
This simulation is useful to ensure that your depth of cut does not exceed the cutting length of your cutter. If depth of cut is greater than cutting length, the yellow portion of the simulated cutter will turn red.