You can only choose one species, which would normally be fine, but I view humanoid species as being able to procreate, and would like to list mixed parentage, but can't.
If there could either be a secondary species linker or the ability to add multiple species, it would address this request.
I don't think there would be other uses, except being able to be more inclusive to inter-species procreation (never thought I'd type that)
More generally, we should be able to add multiple whatevers when we only can add one. A freelance can have two employers (for a secret agent, that's an agent double), an item can make use of several technologies, a priest can worship several gods at once, and a place can even exist simultaneously in several dimensions. Let not WA constrain our imagination and creative freedom ?
I believe this has been rejected before on the basis that technically hybrids count as a new species scientifically - however, having to make a new Species article for every cross-species is still a bit of a pain. I really do think it would be better if World Anvil allowed more than one species to be listed under Species in order to give world builders the option to just link to the species that went into the hybrid. A Secondary Species option (located below Species in the sidebar) could be an effective compromise.
I just count hybrids as a new species, but something like this could still be useful.
I've thought about this before, especially for my characters that are hybrids of two species.