I think the point is that that stranger should introduce himself first in less then 300 chars and then you can decide whether it is important enough to hear him out fully.
Your last sentence makes me feel like you didn't understand the idea at all - it is not to fight spam, but to help you manage communication with real people that you don't know. The basic example is a VC flooded with long copy pasted pitches instead of a poignant and succinct pitch.
