The advantages have mostly been outlined already, so all I am going to say is that you probably wont see a great advantage if you don't do a lot of typing, but if you do there certainly is a lot to be said for the tactile feedback you get from a mechanical keyboard ...and this of course can be tuned to an extent, by choosing the switches used to suite your personal preferences.
My personal preference is for IBM buckling springs, but like many I do use a more modern keyboard now, at the moment a Filco Zero Tenkeyless. This model uses XM White Switches, which to be honest I am not the biggest fan of, I find them a little too stiff, if you really hammer the keyboard they will be fine though, I certainly prefer my Model M. The Filco is nicely made though and I like the Tenkeyless format, helps me keep my mouse and keyboard aligned more comfortably, thu I have persisted with it a good while now, but really I haven't quite gotten used to the force needed for the XM White switches.