text: there are a few reasons...\nto keep the correct volume of gas flowing\nto keep small peices of metal  from flowing with the gas and causing small clogs.\nso you dont cut your fingers and hands\nand most importantly, to make sure when you tighten up a fitting such as a union, or a coupling that you have a good seal (even though you use dope) so you dont have any leaks when you do a pressure test.