do i need the hose that plugs into the manifold directly below the throttle body then goes back into the manifole on the driver side?

what is it for?

 

That line is part of the positive crankcase ventilation (PCV) system. You need it.

 

ok thanks, i was wondering because my friend has an lt1 hes gonna stick in a datsun, and the junk yard that sold it to him pluged it off under the throttle body, and were it ties in to the driverside the manifold they looped it to the brake booster port.

so should i tell him he has to hook lit up to? what would happen if it was plugged off