Not for the current running though the wire but for troubleshooting, safety, and others that may encounter any project. On another forum, a guy completely destroyed a very expensive synthesizer because the wiring colors did not match the polarity, and out of all the people trying to help him, none thought about the fact that the manufacturer had actually used a lot of power supplies which had been wired the wrong way. It will work fine until someone tries to troubleshoot it and says 'Ha! There's your problem, the polarity is reversed!' Say I wanted to reverse the black and red wires on a LED strip connected to a battery, would it still function properly or not? This is also why we have silkscreen on boards, with testpoints labeled like 'there should be 5V here'.

For industrial products it is vital to respect norms and conventions because many people may be involved in maintenance. When you take it apart in five years because it stops working, you will have forgotten everything about the original design, so it really helps to follow conventions. Wire colors are like comments in code, even for simple DIY projects.