For most people it's just what they're used to and you can get by without them. But I do think the addons are an advantage especially in larger groups. If I'm in a group with 10+ people I want frames I can customize which addons give me more flexibility to do. It's like for an afflic lock or any dot-centric dps spec, players can get by without a dot timer addon but most will do better with one over the default ui.