At 100% HP, nameplates are fully transparent, and become more visible as a unit's HP decreases. I find this makes it easier to focus on targets with low HP and doesn't clutter your screen in busy areas like cities.
1.01
Updated for Tidy Plates 5.0 and WoW patch 3.2.
Originally posted by xtoq Good idea, but why not just turn off your friendly nameplates in a city?
True, you could do that, but name tags would still show. This makes them disappear at close range automatically. Plus it's one less hotkey I have to remember. :P