Closed loop question

I'm still new to turbo's so bare with. But i am a studying engineer so i will get it.

-If this is closed loop it reverts the excess psi back into the intake and away from the closed throttle. to prevent it from going back to the turbo.
-But if the excess air is placed right back into the system (im guessing before the turbo), how can it make you run rich? YOUR THROTTLE IS CLOSED?!?
-the turbine will not be spooling hard so that recycled air will just chill in the system.
*Does it mean that the density is whats important. I mean really the air just might run out of the intake filter the wrong way if the turbo isnt spooling.

DON'T YELL AT ME... JUST THINK ABOUT IT?! and then answer nicely