Just got my first gas BBQ and have a real basic q:

Should the tap on the gas bottle be all the way open when cooking? A
quarter turn seems to give the same amount of flame as full open is
(maybe 3 or 4 turns) and I wonder if I'm just wasting gas otherwise.
Maybe once these are open at all the pressure is pretty much the same
no matter *how* open the tap is so it doesn't matter.

Also when BBQ recipes specify time of grilling, do they usually mean at
full heat or moderate?