There is zero advantage in formatting the CF or any other card in camera. As a former Software Engineer this pains me greatly when I read people saying this.
Partly true, formatting CF Cards in camera will not clear any issues with damaged sectors in the card, a full erase or format in a computer will fix them or mark them as unusable. However, a follow up formatting in camera assures that you get the correct file format after you erase a card. The 5D MK III switches to a different format depending on the size of your CF card, and your computer might not be able to do that. The 5D MK III uses exFat for 128gb and larger cards and Fat for smaller ones.
You can do a low level format in camera for SD type cards, so formatting in camera of SD cards is the right thing to do.
Allow me to use your post as an excuse to ask a technical question about 5DMkIII instead of opening a new thread:
You mentioned: The 5D MK III uses exFat for 128gb and larger cards and Fat for smaller ones.
Actually the manual of 5DIII (with firmware 1.2.0 and later) page 54 says: Cards with 128GB or lower capacity will be formatted in FAT format. Cards with a capacity over 128GB will be formatted in exFAT format. HOWEVER, I am not writing this to contradict you. I understand that the second version of the manual is late. I just observed something even different in my case. Both of my 5D3 cameras (firmware 1.2.3) format a 64GB CF card in FAT32 and a 64GB SD card in exFAT !!!!
Have you observed anything similar? I would prefer FAT32 for backing them to my hyperdrive which cannot understand FAT32 even with latest firmware (I have 2 hyperdrive models, they are enough and I do not intend to get the latst which understands them).
I have access to a utility that format's cards in FAT32 and I can create the file structure manually. But I prefer to format cards in camera. I also use MagicLantern and I wouldn't like to complicate things.