PaulS:
It is NOT, and can actually be slower doing it that way.Data is transferred to a byte buffer, which is written to the file when it gets full. As long as there is room in the buffer for what needs to be written, the data is not actually written to the file. When there is not room, or when the close() or sync() methods are called, the data is actually written to the file, and the buffer (and internal index) are reset.
If you try to pre-format a string, the odds of the string not fitting in the buffer go up.
I was asking about the space remaining in the buffer mentioned here. Not the cluster size on the SD card.