You never have to learn fortune telling in order to do magick. Its just that a lot of people choose to learn both and they can be used together. For example, one could use a pendulum to find a lost object in their room after saying a chant to find it. There are several people who will use divination to decide on if they should do a spell too, which sounds more like what you are referring to. This isn't about figuring out if the spell is right, but if it is the right time for you to do the working. I personally, don't do this but I have known some folks who do and find their spells work better if their reading said it was indeed a good time to be casting the spell. So that would be totally up to you if you decide to adopt the practice.