Let's take OSPF as an example. What if you want to configure both IPv4 and IPv6 and use OSPF. You may have to use OSPFv2 and OSPFv3. You also must configure them differently as well.
OSPFv3 can support both IPv4 and IPv6. It also allows the configuration of both of those consistently. This all a benefit for the networking engineer. But there's other benefits for the router as well.
- The entire protocol is now streamlined for both and will be less of a load on the CPU for any of the other protocol independent processes too.
- OSPFv3 running will provide the IPv6 native security features.
Having said this, what if I want to run ONLY IPv4 and ospf can I do OSPFv3? yes... you'll still need to configure IPv6 addresses on the interfaces but you don't necessarily have to use them.