In reply to wilkesley:
Yes, it does make summit day much harder. I think that the reasons are:
The Gouter Hut is crowded, has no running water and smells of poo.
You may sleep better at the Tete Rousse, due to its lower altitude.
It means you can cross the Grande Couloir whilst it is deep frozen and therefore safer.
The summit of MB is so high that you don't need to worry about mushy snow or weak snow bridges later in the day.
From looking at various guiding websites, I think they often ascend from the Tete Rousse and then just descend as far as the Gouter. This means that if you don't make it to the summit, you can then get a second chance the next day. It also then means that provided you have been successful on your ascent to the summit from the Tete Rousse, you can then descend from the Gouter straight down to the tramway and again cross the Grande Couloir whilst it is hopefully still frozen.