Make it a habit to turn your acetylene outfit off at the bottle. Even if it is a pita when you turn it off between uses in the same day, it is worth it.
I was pre-heating a chunk to weld and noticed an occassional acetylene odor. Thought it must have just hung about from when I struck the flame. Came round again, this time I felt the air as it hit me square in the face. I turned it off only to hear it escaping from the crimped fitting at the mixer valve. Had to go back to the bottle to stop it. Otherwise hose is in great shape. Would never guess it would leak at the crimp, especially at such low pressure.
Made me think, if I had forgotten to turn it off when I left the shop, it would empty the bottle in the closed shop. If the air compressor were to start or something that makes a spark,........it could be trouble in a big way.
Always, just get in the habit, turn it off at the bottle when you stop using it. Forgetting the welding shield gas is only an expense as it is non-flamable. But the acetylene,.........whole nuther story.