Is it harmful to my macbook to leave the lid open in sleep over-night for iAlarm? I know it seems slightly naive, but is sleep different when the lid is closed versus open?
There is a slight difference for models with an ambient light sensor.
With the lid open, the sleep light's pulsation will be dim. With lid closed, it pulses at full brightness. Just another elegant design feature by Apple. (I'm not being factitious - I really do appreciate these little touches.)