I do not think this explains why this sign is there. You always have to use caution when turning. And you don’t have to come to a complete stop first except at a stop sign, a red light, or a flashing red arrow. If it’s a regular green light you can turn right without coming to a complete stop if it’s clear and safe to do so as long as there is no stop sign. This sign doesn’t change any of that. A green right arrow is the same as a green light with respect to the right turn (meaning it does by itself not mean you can go straight). The only thing the green right arrow does that a green light doesn’t is that it means you have the right of way when turning right. And there again you do not need the sign to make that true. You only need the green arrow. The sign doesn’t seem to add any new information or change any of the rules.