If we were working down the hall from each other I could pop my head in and ask you a quick question with enough extra social context (tone of voice, energy level, volume, facial expressions, etc.) to let you know I respect your time and just need a quick answer on something, not a full conversation, and that if you look busy and give me a short response, I won't be offended at all.
If I delivered that very same question via email, since you're a nice person you would wonder whether I would be offended by a curt response, and to err on the safe side you might spend more time answering it than I intended to ask you for. Then I feel awkward for having asked it, and there's awkwardness all around.
The problem is the age-old textual deadening of social cues, not this poster's solution, I think.