Halliday & Matthiessen (1999: 545):
We have suggested that the immediate context for this change was a discursive one: the evolution of a register of experimental science, in which certain forms of argumentation were highly valued. This is usually interpreted simply as the emergence of a particular genre, the scientific article; but that is only one side of the story — no such genre could have come into being without these changes in the grammar of the clause. At the same time, they have other significant consequences.
We have already pointed out the fact that one effect of grammatical metaphor is to render many of the semantic relationships implicit: if the happening is construed as a clause, the semantic relations are spelt out in the configuration of grammatical elements, whereas if it is construed as a nominal group they are not, or only partially so (compare his energy balance approach to strength and fracture with he investigated how strong [glass] was, and how it fractured, using [the idea that] the energy [...] balanced out).
On the whole, the greater the degree of metaphor in the grammar, the more the reader needs to know in order to understand the text.