They have two bomber clip-in points. This means you can haul stuff in them on overhanging terrain and/or clip them under the haulbag. The big clip-in points are easy to grab and handle (you don't worry about dropping your food bag when pulling it out of the haul bag).
They are burly and tough enough to be used as a rope bag. I use them for just about everything. The big size fits a lead rope or a big sleeping bag. The medium size is for a normal sleeping bag and three days worth of wall food. The small stuff sack is great for personal items. I find the largest the size the most useful.
The alternative to this bag (just using a normal stuff sack on a wall) is not fun. You have to tie extra knots in your stuff sack draw cord and even then it can be a little nerve racking to hang valuable items off a little piece of drawstring.
These are heavy. If you are saving grams or looking for an ultralight setup, this ain't it.
These are expensive. However, they last forever. So they are a great long-term value.
These are ideal for big walls. But they are also great for any application where you have burly items. I put my drill kit in one, I use one as a big wall rope bag, I store my rope in one. There are lots of applications.