It is there to bleed the system when you change the fluid or open the sytem. It is a pressurized system, unless you are overheating due to air pockets in the system I see no reason to routinely bleed the system. My plastic screw broke and no one had touched it for 10K miles.
If you do tighten it make sure it is just enough to stop it from leaking they can break.
Some people dream of speed-others create a damn jet powered shopping cart.
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