What's the point of the first action in double-acting baking powder? Modern baking powder is basically always "double-acting". This makes a lot of sense compared to the older single-acting powder, since the gas formed during baking won't be removed by mechanical actions like pouring batter into a dish, and occurs when the starch is ready to form a gel, stabilizing the foam.

So what's the point of the room-temperature reaction? It doesn't seem like there's any particular point in producing gas immediately, compared to during the baking process.

Note that I'm looking for documented reasoning from manufacturers or food scientists, not people's informed guesses or personal opinions.
The first "action" is when it gets wet. This is the traditional baking soda + vinegar fizzing. The second rise in double-acting baking powder is when it gets hot. 

In a baked item, such as a cake, this reaction to mosture helps create rise immediately, before the cake starts to change structure, solidify, and form a crust. This enables the center to begin to rise immediately. Without this initial rise, the outside of the cake could have already started to form a crust before the inside is heated enough to rise. This would result in "trapping" the center--either causing a denser unrisen center, or breaking/cracking the crust as it rises and escapes the crust.