[maroun]

When you first see sunlight in the mornings it helps regulate your circadian rhythm and it tells your body "The sun is out this is when I should wake up". Which is why if you're traveling you want to make sure you wake up at the right time locally and open the windows right away, it'll help reduce the # of days in which you're jetlagged.

However if you're sleeping at home you want your body to sleep for as long as it needs to, uninterrupted. That means no sunlight, no noise and no alarms. If you get into a consistent schedule you're body will wake up at around the same time everyday. However if you have sleep debt that you need to make up, you also want to give your body the chance to sleep a little extra.