Kubernetes isn't even necessary for medium and large businesses. It's more a question of what problem you're trying to solve.
Kubernetes is only relevant if you have the need to scale your service quickly and/or often. If you run it on your own hardware the value is even more tricky to work out, it can still be a benefit. Whether or not it help you save on hardware cost is extremely dependent on your usage.
I see it as decoupling the system administrator tasks from the software tasks. Sys admins can setup the OS, volumes, kubernetes, and monitoring processes. Application developers can do their own thing and deploy apps without having to care about the details of which mount their app needs for disks or the intricacies of whichever process runner they use.
Kubernetes is only relevant if you have the need to scale your service quickly and/or often. If you run it on your own hardware the value is even more tricky to work out, it can still be a benefit. Whether or not it help you save on hardware cost is extremely dependent on your usage.