Simple. Lightweight. NeedToKnow is for minimalists.
Simplicity of function
NeedToKnow is a timer bar addon.
NeedToKnow is intended for your most frequently monitored abilities. NeedToKnow is for your rotation. It's NOT intended as a general buff/debuff addon. If 4 groups of 6 bars is not enough for you, you want a different addon. You might also want to rethink your UI.
Features should be opt-in, not opt-out.
Simplicity of appearance
NeedToKnow is intended to show you the most important information—and ONLY the most important information—at a glance. The idea is that the only things you want moving or taking up screen space are things that are important.
The bars don't move locations so that you always know where to look to know when you need to refresh a DoT or short-term buff. You don't have to search through a stack of bars to find that one important one.
Cosmetic features should reinforce, and not distract from, the visibility of most important part of a bar: its length.
There's no reason a minimalist addon shouldn't have a minimal effect on memory and CPU usage. CPU usage in combat is the most important metric.
Simplicity of configuration
Users see this a significant feature, especially compared to addons like PowerAuras or ForteXorcist.