> Devirtualization helps performance because you are able to benefit from inheritance and not have to pay a performance penalty for that. Without the final keyword, a performance oriented project would need to be architected to not use inheritance at all, or in the very least in code in the hot path, because that sneaks gratuitous pointer dereferences all over the place, which require running extra operations and has a negative impact on caching.

virtual inheritance. Regular old inheritance does not need or benefit from devirtualization. This is why the CRTP exists.