If there is wind, I know that leaving your kite inflated will damage the trailing edge of your kite over time in the same way the wind weakens the material of a flag. I have had two kites that I have left in the wind too long as I relaxed between sessions. And, over time, the trailing edge began to come apart/rip and I had to have the trailing edge reinforced.
But yes, it is very nice to wake up to an inflated/ready to be flown kite. So perhaps it is well worth leaving the kite inflated!
(As far as damage to the bladders/valves, I am interested to see what people say as well).