Can someone offer an explanation of why all the alternative processes state hard gelatin (photo grade) has to "bloom" before it can be used? What's going on during this cold water phase? That is, why is it necessary for gelatin to sit in cold water for so long before it's finally heated up and goes into solution?

I've let gelatin sit and bloom, and then I've also taken the gelatin granules right out of the container and dissolved it in hot water right away. It works both ways (I use it as paper sizing). I'm curious, what's going on during the blooming step and why is it required?