If you’re someone who doesn’t want to spend ages trying to move your UI elements around to look just right, this is the addon for you. It’s popular because it’s easy to set up and looks great from the start. ElvUI is the slick-looking unit frames that you probably see in most screenshots. One of the most popular unit frame addons for the live game is available for Classic too. There’s a few addons out there to make your life in Azeroth a lot more manageable.
The default Blizzard frames can be troublesome, and they lack the ability to show stuff like debuff timers. If you need to clean up your WoW Classic unit frames for easier play, you should consider getting some addons.