My thought process was that fields with a small number of bytes (< 8, maybe < 16), the field displays better with a space in between bytes. Some fields however are variable length between "something small" and "something large", which may be "situation dependent". It's for that reason I think a preference could be used to aid in displays for situations where the byte fields are always small.
With the recent addition of different "byte BASEs", a BASE_SPACE could certainly be added to fields known to be a small number of bytes, and have the decision to "hard code" spaces into that field could be left up to the dissector developer. But I think that's a separate patch and both types of functionality (preference + dissector choice) should be available.
Michael
