Using the Daylite will reduce the amount of things you can carry in the pouch, but not eliminate it. I use the pouch to carry my Megalite or Hubba Hubba (out of their stuff sacks) and putting the Daylite on does not really impact it much. It really depends on how stuffed you have the rest of the pack to.

One thing to consider is that you will not want to put heavy, dense stuff like camera gear that far away from your body- it will affect your comfort. I would reccomend using the Daylites capacity for clothing or tent and use the toplid for your camera gear.

Hope this helps,
Christo