How do you decide what byte[] size to use for InputStream.read()?

When reading from InputStreams, how do you decide what size to use for the byte[]?

int nRead;
byte[] data = new byte[16384]; // <-- this number is the one I'm wondering about

while ((nRead = is.read(data, 0, data.length)) != -1) {
  ...do something..
}

When do you use a small one vs a large one? What are the differences? Does the number want to be in increments of 1024? Does it make a difference if it is an InputStream from the network vs the disk?

Thanks much, I can't seem to find a clear answer elsewhere.