The Princess Sleeps ...
Is it a good idea to sleep in on the weekend? I do not think so. All it does is disrupting a sleeping pattern and stopping you from forming the habit of getting up at the same time in the morning.
Habits are there to help us to accomplish things. They reduce the amount of deliberation and willpower needed to get into some form of action – like getting up at 5:30 in the morning.
On the other hand: If you are lying in bed, you can at least not order a new encyclopedia to further crowd your already crowded bookshelves.