Originally Posted by
scher
With a frame bag you have versatility to carry anything you like - including bottles. Look at all the wasted space around the bottles and cages. You could stuff clothing and snacks and other stuff in there if you needed to. With the cages you don't have that option.
For me this was a big part of it. My frame bag holds my tent, air mattress, sleeping bag, and bag liner, that's a lot of bulk in an out of the way place. With clothing in the seat pack and cooking in the handlebar bag it makes for a good layout and easy to find things.