Why use Consul with Kubernetes, Docker, Mesos?
It's simple - it depends on your application. If it needs those features Consul have, and which other systems don't, then you can go for it.
Besides that, there are a lot of Hashicorp products tightly integrated with a Consul in part of HA. Vault, Nomad and Terraform. Consul can be used like a variant of ZooKeeper, but Raft based. We use it that way.
Another concern, maybe you would like to have another layer of indirection in your system. Consul cluster can stand for verifying connectivity between various remote parts and etc.
So, it's not about how big is the advantage, it's about your very specific requirements and limitations in your very own moment.