In this example from Book of the Dead, vertex shader wavefronts appear in green. Pixel shader wavefronts appear in blue. On the bottom graph, many vertex shader wavefronts appear without much pixel shader activity. This shows an underutilization of the GPU’s potential.
If you’re doing a lot of vertex shader work that doesn’t result in pixels, that may indicate an inefficiency. While low wavefront occupancy is not necessarily bad, it’s a metric to start optimizing your shaders and checking for other bottlenecks. For example, if you have a stall due to memory or compute operations, increasing occupancy may help performance. On the other hand, too many in-flight wavefronts can cause cache thrashing and decrease performance.
Source: Unity Technologies Blog