I think an advantage would be being able to put more intensity into each workout. Eg. if you usually do chest and arms in one workout, if you did chest in the morning and arms in the afternoon you could use more intensity on arms because you would usually be tired after chest, especially if low on carbs.
Also, I think working out twice a day would boost your metabolism somewhat.
If I was doing this it would look something like
Day 1 - Morning - Chest
Afternoon - Arms
Day 2 - Morning - Quads
Afternoon - Hams and Calves
Day 3 - Morning - Back
Afternoon - Shoulders
Day 4 - Rest
Day 5,6,7 - Repeat
I may get pretty burnt out doing that, especially with cardio aswell.