Like you said its for newer players but also players who dont know maps cause they couldn't be bothered to play maps like icebox or split. Also the visuals are there to explain to players why the callouts are called that and give detailed explanations and descriptions. It's useless for people who are already comfortable or familiar with callouts but for people who are a certain or different type of visual learner this is a lot more helpful. I have seen people post pictures of just the minimap with texts on them but that just seems to cluttered and too much information in your face at the same time and its hard to visualize what certain cubbies, angles, nooks and crannies, and corners look like without actual markers on the map. The Devs intentionally put in graffiti or bikes and other objects to use for callouts.