Halliday & Matthiessen (1999: 505):
This is not to say, of course, when a choice is made among a set of alternative descriptions for representing features in grammar that are inherently indeterminate, like the types of process in a transitivity system, that the choice is insignificant, or merely random. On the contrary: it resonates through the grammatics as a whole (or should do, if the description has any claim to be comprehensive). Again there is the analogy between the grammatics and the grammar: just as no region of the grammar is isolated from the rest, so every descriptive statement has consequences throughout the description.