Yes, it would need it in life and in competition, agility, or schutzhund. It is always better to ask your dog to sit and remain in sitting position in any awkward situation with another dog, they calm down faster whilst sitting or lying down. You may need to walk into some shop, to some object or person leaving your dog waiting for you. Start training him patiencer by walking away from him short distances first, then longer, walk around him, ask him to wait longer. Ideally, your dog shouldn't change his position until a new command was given. Train him patience when throwing the ball, throw his ball, ask him to sit for couple of minutes, then send him after the ball. "Stay" is normally supported by gesture of your hand outstretched like in "Stop".
Without knowing it well your dog wouldn't learn "Freeze", when he must freeze in the middle of the motion, all in all, "Sit/ Stand/ Down, Fetch + Stay" works as intermediate command before learning some more difficult commands. You simply stop pronouncing it after a while when your dog starts to understand that he must remain in whatever position he is until you tell him something else. It demonstrates how well you are in control of your dog.