This 3/8 to 8mm elbow has a couple of great uses.
1) If you choose a 3/8 outlet regulator - this will allow you to have the gas pipe comming out at a 90 deg to the Reg.
2) It is a direct replacement for the JIC elbow on the tanks fitted 80% shut off valve, and connecting 8mm is a simple compression / olive fitting. So rather than use the big, expensive JIC fill hoses on your GAS IT, Gaslow, Caratank and any gas tank with the JIC elbow on it, then this item is a perfect direct replacement to allow you to use 8mm copper to fill either our GAS IT tanks or GAS IT bottles. It will even replace the Gaslow fill elbows.
It allows more convenient pipe runs for filling, as you can use any length of the specific approved copper 8mm pipe.