Answer:
Gas welding basically used for weaker joints(in sheets) and arc welding for stronger one(plates).
mobile welding (not in a shop)is the ideal time for arc welding . gas welding is the way to go as far as production is concerned , but requires environment with little air circulation or wind , plus gas bottle , machine , and a short lead , which makes it ideal for shop work
answer
Gas welding - generally use for welding of thin plates/pipes. Less heat input and less likely to burn off the edge of the plates (undercut). It is a more expensive process because of gas shielding.
Arc welding - use for thicker plates usually with larger size electrodes. Higher weld production rate. Shielding by means of electrode coating.
Both processes can meet the required mechanical properties usually