>>2272294Most of them, you're able to remove the main pack and either attach/jerryrig another one or use it to carry other stuff easier like firewood without it cutting into your back/fabric. Pic related is a Kelty external frame I removed the pack and put on a Polish rucksack. Weaved the straps through the frame to help hold it tighter
That's another thing; the frame it's self allows you to easier attack straps or odd things to it. If could a meme like Sam's pack in lord of the rings with cups and stuff but realistically its that one or two bulky/rigid thing that wouldn't fit inside too well
I prefer the space the external frame has over an internal (and I do have/use both) because in most cases for me having too much fabric snug around you is like not layering and instead wearing a big coat
>Tl;dr: external frame gives more options 