I've looked at the midi file spec, and it refers to this value, says the default value is 8, but doesn't really say what would happen if it was set as something else.
I've looked at a number of different midi files, and this value is always 8. I could look at a LOT more files, but .....
The 'resolution' of the midi file, as regards midi data, is set by the 'Division' parameter in the midi file header, and I looked at files with this set as 120 ticks per quarter note and also 480 ticks per quarter note, and both of these still had the 32nd notes per beat set as 8.
If you're really concerned about this, you might try changing an existing file from 8 to, say, 32, and see what happens?
However, if a quarter note is 120 ticks, then an 8th note is 60 ticks, a 16th will be 30 ticks, a 32nd note 15 ticks and a 64th note (is there such a thing ?) would be 7 or 8 ticks (would you notice the difference ?) and I assume this could still be resolved from normal midi data. If the 'division' setting was 480 (commonly used) then the note resolution could be even finer