If this fixes your problems, reinstall your addons one by one. When you next start WoW, the folders will be recreated. Rename the Cache, WTF, and Interface folders, to whatever you like. As the video says, exit the game, and open the containing folder of your WoW installation. Why rename them? Don't you usually delete them? Well, you can certainly do that, but if the reset doesn't fix your issues, renaming them will mean that your settings can be restored to how they were before.

They're not talking about a simple /reload UI, which can be typed into the chat box, rather about renaming your Cache, Interface and WTF folders. If you're suffering from high latency, low framerates, disconnections or similar issues, resetting your interface is worth trying before attempting more extreme measures. Blizzard's Customer Support team have posted the latest addition to their WoW Tutorials site, this time it's a video filling you in on how to solve your WoW technical issues in 60 seconds or less!