I have got what proxies are for, I know how they should be made and used, but one question persists, when?

All I want is to get an idea of when I should start to think about putting things, and what things, in my proxy classes. Can you give me examples to get the idea?

So basically, I should register renderers and keybindings and client-side configs in client proxies?

That makes the use of server proxies only for multiplayer, but it does make sense to me since the proxy instance has to be something and Minecraft processes with integrated server are clients too and need the client-side code.