I have some pain in my hands so it will be short and quick. Many users prefer keyboard to the mouse. Many developers i mean. So far keyboard support in Unity has not been the best it could be. It does not have a standard OS framework based UI and it is a graphical tool for designing game levels and its roots are deep in OSX so it is understandable that the engineers behind it did not add lots of keyboard navigation support to it.
Other than liking there is a big issue. Some people (like i myself recently) start to have problems in their hand due to extensive mouse usage. For me it is limited to Unity and Web browser usage and only once in a while a bit in visual studio (reducing it to 0 by learning all hots). In these cases not supporting full keyboard navigation for at least doing hierarchy, inspector and project view modifications means being able to work or not. It's at least like that until you get better.
Unity has hots and some of them are very useful but for example when you focus the inspector with CTRL+4 , navigating to each field is not easy. Skipping to the next component, adding a new one without touching the mouse or using the menu bar (component menu) is not even possible AFAIK. This can be fixed easily i guess and I'm asking Unity developers to kindly do that. I am not saying modifying scene view should be possible without touching your mouse but doing something like making a new GameObject, Turning it into a prefab and setting some values in its inspector (including gameObject fileds) should be supported. Quick question, How do you change between assets or scene objects in an object picker window using the keyboard?
While doing this you'll make unity more accessible for the people who have mouse control issues as well and you'll make many developers very happy. Also you'll make it less likely for someone to have reduced health due to extensive mouse usage. Honestly I don't know how is the stae of these things in other commonly used engines like UE4 but the same thing defiantely applies to them as well. I did not mention because I can not ask for something which i don't know if it exists or not.