what are the pros and cons for piping with buttercream and piping with royal icing? I know royal icing will dry harder... but what are the other advantages?

The reason I'm asking is because I have a wedding cake 2 weeks from now, and it involves fairly detailed piping.. nothing crazy though. And I don't know which to use...

Any suggestions or help?

Thanks CCers!

Also depends on the surface on which you are piping. I prefer to pipe BC on BC and RI on fondant.

You can pipe much smaller details using royal icing. Like another poster said I use BC on BC and royal on fondant.