Ode to the comma

There has been many an ode to the comma written. I've even heard people say that a comma can save lives! Consider this simple sentence.

Let's eat Grandma!

Let's eat, Grandma!

It's become really interesting for me, because I am an American living in Ireland and writing for the British market. I try to stay away from colloquialisms. But confounding the issues is the fact that styles can be markedly different for English of different countries. The comma being one of the culprits.