I have an $800 spectra mountaineering pack and it has daisy chains are on the top pocket. Since its spectra the weight is very small, but they provide a place to attach anything that you might want to, like strapping a pad or tent above the top pocket. If you wanted a strong attachment for something and they weren't there it would be tough to add them. Originally they were for hanging serious climbing gear where you might be able to get to it, like if you need a piece of gear and its inside your pack and you're hanging over a precipice, it won't do you any good. They were more from the age of pitons. I do have a BD piton hammer, but it would hang from a loop around my shoulders. My climbing pack has 2 holsters on each side for ice tools or hammers. Oh it also has daisy chains all the way down both sides, but the modular straps and accessories all attach or run through them and they provide positive support, that is they keep things in place.
On most packs they offer a place to slide through auxiliary straps to strap a coat or garbage bag or shovel to OR TENT!. My climbing pack has a specialised shovel pocket that is modular.
Jim