Like anything else, Node-RED is a tool. You don't reach for a hammer when you need to unscrew something.
Node-RED is useful for prototyping. More than that, it lets you build quickly so that you can let it do all the boilerplate you've have to write if doing things purely by language. Letting you focus your programming skills on the more interesting and involved bits of logic.
You can still use JavaScript and I will often write function nodes because I find that quicker and easier to write than messing with loads of nodes. The nodes do the setup and generally the basic comms - which are really involved when doing it by code - the functions nodes do the core "business logic".
Best of both worlds! (Assuming you are happy using JavaScript!!)
