k1n9k00p4 totally missed the point here.. An allocation unit is not a partition.
You should stick with the default 4K cluster size - this will allow you to use compressed folders (compression is not supported for anything above 4K). Also, the memory page size is 4K, so the swapfile will fit nicely with your filesystem.
Use bigger cluster sizes for data volumes with big files (a movie partition perhaps?) and smaller for zillions of files (an email server maybe?).