I have both the lid and the hip belt pocket for my Unaweep 3900. I like them just to have a little bit of organization. The belt pocket (smaller one) is perfect for things you want quickly without taking your pack off. Even the small one will easily fit a snack bar, pocket knife, cell phone, etc. Pretty sure it’s only 2 ounces or so in the smaller size and still bigger than most belt pockets. I tried the huge one. Just too big for me. Same thing with the lid – not necessary for space really, but great for organization. Wallet, inReach, car keys, charger – loose critical stuff like that lives up there. Those are odd things that I prefer not to have hiding in the bottom corner of my pack somewhere. Lid is only 3 ounces so worth it in my opinion. The connection system could use some re-thinking, but it works.