You have already been informed on the set-up. OTOH, the reply, "Set the fuel tank and fuel lines up properly and you would never need to use one." I find that reply a bit restrictive when using "Never".

I use Header or "chicken hopper" as they may be termed fairly frequently to assure good fuel flow.
The #1 time is when a fuel tank is tight inside a small fuselage area without adequate padding. It is easy to get fuel foaming which wrecks havoc on good operation. Another time is when in a rather large model, the tank is not in a really good position to assure good flow, especially to some of the glow engines that require significant pressure to maintain the Needle Valve setting, those engines that have overlarge Carb. ventures.

I have a SPAD with a gutter pipe fuse. that is fun to fly. It is the standard .40 size, but I use a .60. I could only fit an unpadded 6 oz. tank in the fuse. so I use a 2 oz. header outside with 1/2" rubber pad. Works great. More fuel and the foaming doesn't get to the header. I also used a header in a large model with a Webra 1.20. Unless one is using a bladder tank, I find the header an effective alternate based on the situation.