Generally, we don't want to put everything into ONE card, the memory card is short term storage device for us to hold the recorded images/video and we need to transfer them to computer ASAP.
unless you can fill up more than 75% of the memory card within a shoot, else it is not justifiable to use such large capacity card.
if you only one piece of large capacity memory card, and don't delete transferred image/video from the memory card after you downloaded them, you will only have part of the full capacity to store new images/video, than what is the benefit of using such large capacity memory card?
if you usually shoot around 24 GB of stuffs in a shoot, it is better to have a few 32GB cards instead, let say once the content from a shoot is downloaded to your computer, you can leave this memory card with images/video aside as back up copy, and use another blank memory card for next shoot, and do the same for this cards.
so by the time you need to reformat a memory card from the previous shoot, probably you have already finished with post production of the previous shoots and don't need the back up image/video in the memory card any more.
External memory cards work with FAT32 file system. The specifications are open and can be found online
Check http://en.wikipedia.org/wiki/File_Allocation_Table#FAT32 (The column on the right hand shows the details summarized.)
Even with smallest cluster size the maximum volume size is 2TB. It will take a while till memory cards reach that size.
I agree with catchlights here: get a few smaller cards instead of one large one. I still use some 4GB cards that I got years ago, they still serve me well. Together with a few 8GB cards it gives me plenty pf space for my images. I wouldn't want to replace them with a single card of the same volume.