As Marx said, you get a tiny amount of Codex Entry credits to cash in, if you actually scan the geological features in question with the Composition Scanner. Only one of each type of object per system counts. As you need to be within a few hundred metres for the Compo Scanner to work, it's not usually worth it, just from a getting-credits point of view. But if you're planning on landing to refill Mats anyway, you might as well do the Compo Scan thing. Or you might just be trying to complete your Codex scan collection, in which case getting the Compo Scans is your primary mission.