In my very limited beginner experience the compositor is useful to know and be able to use even if you don’t need colour correction and/or green screen.
You’ll realise it’s usefulness when you need to do something in a project – your desire to have only bloom applied to selected emission materials is a case in point.
In my case it was to get shadows from the plane/ground you add to you viewport but then switch out this background and keep the shadows.
Recently I had another problem where I wanted to mask out an element of an object from my render which I could do with a holdout shader but that also masked the background so I needed to composite the masked render back to the background layer. Being able to do this within the render is so much more efficient than rendering out 2 files and manually putting them into photoshop cos you’d have to do this every time you re rendered
