Pardon my ignorance but why would you need an app to manage keyboards and mice in the first place? Aren't they supported out of the box by generic drivers?
In general, custom configuration on both mice (DPI, refresh rate, etc) and keyboards (tactile response settings [See https://wooting.io/], hot binds, etc).
It's a nice to have (almost to the point of necessity) especially when you go to LANs and need a consistent way to load your settings on a computer that's not yours.