This is useful for hybrid systems which exploit shallower analyses when deeper parsing fails, or which try to match deeply parsed queries against shallow parses of large corpora; and in fact, RMRS is gaining popularity as a practical interchange format for exactly these purposes (Copestake, 2003).
rMrS is still relatively ad-hoc in that its formal semantics is not defined; we don't know, formally, what an rMrS means in terms of semantic representations like (2) and (3), and this hinders our ability to design efficient algorithms for processing rMrS.