the monarchy and the way it links past, present and future in one apolitical and unambitious person
I think at one time a monarchy would have been good for Poland which badly needed a figure in situ who stood above political divisions.... (JPII was the closest but he was not physically present in the country enough). It's too late now but it could have made the late 1990s and early 2000s a lot more civil.
I think the monarchy was very good for Spain after Franco (and the King's taking a stand against the 1981 coup attempt gave the monarchy legitimacy for a few decades which he ultimately p[ssed away)