There are both pros and cons each way, for me the pros of having it in my bag outweigh not but each of our pros and cons will differ. I never take my bladder out of my bag except for when I'm disinfecting it in the off season.
It takes up minimal space in any bag over 3000ci. I prefer to fill my bladder while it's in the pack and not mess around with removing it and I like it to hang so that the weight is placed higher on my frame and not sagging into a pocket.
It takes up minimal space in any bag over 3000ci. I prefer to fill my bladder while it's in the pack and not mess around with removing it and I like it to hang so that the weight is placed higher on my frame and not sagging into a pocket.