I don't know exactly how it works, but I think it's a good thing talking from the point of view of someone who lives in a different form of governament. Let me explain how I see it, and bare with me because - as I said - this is just how I see it from the outside...
I know that a Constitutional Monarchy is a government in which a monarch acts as head of state within parameters, but the monarch does not have any real power. The Monarch cannot make or pass legislation and has to stay politically neutral. He?She's the Head of State and he/she has to perform official duties, but has to acts on the advice of her elected ministers.
So, basically. I see the Morarch just as a figure, not as someone that has a real power (but I'm sure he/she can still do a mess if he/she wants) that is there as something for the people, a connection to a different time! To me it says that the State in question is proud of its past, and the decisions it made, and the crown is a reminder of how great the Country was and still is... (without giving a crazy ammount of power in the ends of just one person).
I uderstand it can cost a lot of money to "take care" of the Royal Family, but these money would end up being spent for other frivolous reasons... (I come from a place where politicians like to waste money around or put them in their pockets) but it also gives a Status to the Nation somehow... From the outside I see it as a sign of greatness!