Number: 8 (coarse) 40 (fine)
The device's stereo balance (assuming that the device has stereo audio outputs). If a MultiTimbral device, then each Part usually has its own Balance. This is generally when Balance becomes useful, because then you can use Pan, Volume, and Balance controllers to internally mix all of the Parts to the device's stereo outputs. Typically, Balance would be used on a Part that had stereo elements (where you wish to adjust the volume of the stereo elements without changing their pan positions), whereas Pan is more appropriate for a Part that is strictly a "mono instrument".
14-bit coarse/fine resolution. 16,384 possible setting, 0x0000 to 0x3FFF where 0x2000 is center balance, 0x0000 emphasizes the left elements mostly, and 0x3FFF emphasizes the right elements mostly. Some devices only respond to coarse adjust (128 settings) where 64 is center, 0 is leftmost emphsis, and 127 is rightmost emphasis.
Note: Most all devices ignore the Fine adjust (#40) for Balance, and just implement Coarse adjust (#8) because 14-bit resolution isn't needed for this.