I like to leave them open a bit to get the morning light also. But that really depends on whether or how many street lights are shining in the window at night. Too much light does bother me.

Once when I stayed at a place in San Francisco, I didn't realize my room was just under the building sign until nightfall . They had a 5-billiion lumen floodlight on the sign, which unfortunately also shone directly in my window. Argh.