Six years in and I’m still learning every time I sit down to the harp. Musicianship is a constant learning process, and I doubt there will be a moment where you feel you’ve “learned it”. More specific to your question though, sight reading can help you test how comfortable you are with the harp, as well as improvising. When there’s no prep work in advance, how comfortable are you? With no sheet music? Try it out 🙂