from switch evolution:
We have implicitly assumed that Layer 3 switches also provide Layer 2 switching functionality, but this assumption does not always hold true. Layer 3 switches can act like traditional routers hanging off multiple Layer 2 switches and provide inter-VLAN connectivity. In such cases, there is no Layer 2 functionality required in these switches. If placing a pure Layer 3 switch between the Layer 2 Switch and the router. The Layer 3 Switch would off-load the router from inter-VLAN processing.
the Layer 3 switch is really like a high-speed router without the WAN connectivity. It don’t has WAN interfaces. This means that the Layer 3 switch is really for large Ethernet networks that need to subnet into smaller networks. Most of the time, this is done using VLANs.