Can you imagine the cost of electrical work if an electrician actually stopped to label the wires? Woah. Generally speaking there are standards, and if you work around this stuff day in and day out, you don't need labels. Though when you have a mass of wires coming down a conduit it's nice to have those tagged so you know where they're coming from. At the very least on the panel so you know how to turn off branches. Which you did before working on the wires, right Matt?