We do that with other stuff too. Twice fried chips (i.e. thicker french fries) are incredible.

Actually, that makes sense now that I think about it. Twice fried chips involves frying once at a lower temperature, and then again at a bit higher temperature. I imagine this is what's happening with toast too, as I'm pretty sure the toaster is operating at a higher temperature than what the bread is baked at. We want the exterior browning of the higher temperature, but we also need the bread to rise properly in the oven.