Maybe I just don't trust the smoothness of my derailleurs, but I would never switch down to the little ring at a stop sign if I was expecting to be back in the big ring once I accelerated. I'll go to a big cog and cross chain as I start off, but then run down the cogs pretty quickly to whatever gear is right once I hit my stride. I seldom want to be going from the little chain ring to the big chain ring whilst I'm accelerating, the extra moment of hesitation just isn't conducive to acceleration - except maybe at the crest of a hill.