Question / Help can someone explain the noise gate to me??

ive seen videos and read about it but theres still some things im not understanding. why is there an open and close threshold. why isnt there just one meter. and when the audio is under the bar i thought the audio is supposed to cut off. on my preview the audio is still capturing even thought its under the bar
 
ok so i fixed one thing. the audio wasnt cutting off cause i had to stop previewing stream then start the preview again. now the only last thing i dont understand is the point of 2 thresholds
 
Close threshold = Anything below this will be cut off (mic off).
Open threshold = Anything above this will be picked up (mic on).

Why there's two is probably for increased control. It works so that's good.
 
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