Tidy Plates is a simple addon that replaces the default nameplates with a clean, simple nameplate interface. One of the major differences between the default nameplates and Tidy Plates is that Tidy Plates prevents the plates from overlapping. This ensures that all plates are visible at all times. A major option with Tidy Plates is the variety of themes available (see the screenshots on the Curse page for examples).
The real reason I use Tidy Plates, though is that it shrinks or grows the nameplates based on whether you are in combat with the creature. For example, if you are running past a mob that is not in combat with you, the plate will be small. If you run too close and the creature attacks, the bar grows large and flashes, letting you know that it is attacking. Combined with an optional theme, Threat Plates, I felt secure in uninstalling the often-recommended Omen threat meter. Threat Plates takes the shrinking and growing feature and uses it to inform you of your relative threat level on all mobs via their nameplates.
Threat plates has 2 modes: Tanking mode and DPS/Healing Mode. The difference is simple. In tanking mode, the nameplates change color and size based upon losing threat, while DPS/Healing mode changes size and color based on gaining threat. In both cases, a small gray-bordered bar is secure, a medium-sized yellow bar is insecurely-tanked, and a large flashing red bar is bad. In a tank’s case, it means you’ve lost aggro and need to taunt. In a dps/healer’s case it means that you have gained aggro and need to dump it before you’re eaten. While this may sound complex, it is actually quite simple, visually. Regardless of mode, the theme is designed to highlight mobs that need your attention by making them larger and displaying a warning color (yellow or red) to mark the severity of the issue.