Increased range or/and extra heavy payloads. It was detachable when empty just like a droptank but did not occupy a hard point. Remember soviet factories were out of range, but with this it could be in range. No it was not a silly thingamabob.
Well it looks like a 300 liter drop tank. Can't imagine THAT did much for range, especially with this inherent drag. Now if they where going to scale it up like you suggested, that might be something different, but I have only seen this setup.
Regardless, still think it was ridiculous. And it looks like I was right! Hey, how about that? Well even a broken clock is right twice a day! Woo Hoo! Victory lap around the kitchen with a moon pie in my hand!