Halliday & Matthiessen (1999: 270-1):
There is a loss of experiential meaning, since the configurational relations are inexplicit and so are many of the semantic features of the elements … There is a further loss of experiential meaning, since the categories of experience become blurred … the construction of reality becomes a construction of unreality, detached from ordinary experience and hence inaccessible and remote. …
There is however a gain in the potential for experiential information, because the participant, more than any other element, can be expanded in respect of [sic] a wide range of semantic features; this enables anything construed as a thing to become part of an experiential taxonomy which embodies far greater generalisation about the overall nature of experience.