In the United Kingdom and the Commonwealth Realms, it is the ultimate defence against an elected government deciding to act despotically.
It's the final check and balance that ensures stability by allowing a government that acts illegally or unconstitutionally can be removed from office.
Because it exists, it is rarely needed - but twice in the twentieth century, in Australia in 1931 and 1975, the Crown removed a government from office when it tried to exceed its legal authority. And it was done peacefully and smoothly. And order prevailed.
Yes, part of monarchy is purely symbolism - but that's not all it is.
I've sworn oath to the Queen - both as a symbol, and as ultimate constitutional authority in the two countries I am a citizen of. Both things matter.
Just out of curiosity, how did you feel about the Queen endorsing the “Gay Marriage” decree?
And how will that work for the continuity of the Royal Family if an heir is “gay” so he/she can’t reproduce the old fashioned way?
Just wondering....