a bit more on my reply.
for the non-believers, sleeping altitude, let's say 10,000 ft, is important because
(1) if staying overnight you obviously spend more total hours of the day at height
(2) importantly, when asleep your respiratory rate falls, your oxygen saturation falls ( even worse if you have sleep apnea at either sea level or up high). Thus, your "effective" altitude rises, and the resultant stimulation of the acclimatization process is improved in a more gentle way than huffing and puffing all day long.
