You should try it. It's fun. But hard.
To chose some music you've already created/composed/recorded and try to fit it to a scene could be pretty easy, but looking at a scene and try to imagine what kind of music that needs to be composed and would go well with that is a completely different thing.
Just by choosing a particular mood of music could change the whole scene. A woman walking through the woods with some light, happy music makes the scene light and positive, but change the music to something darker and you might get an thriller/suspense type of scene. And not a killer in sight! Just different notes/instrumentation.