Eats shoots and leaves.... Is this a hungry gunman or a description of a panda bear? It depends where you put the comma:
Eats, shoots and leaves - definitely a hungry assassin.
Eats shoots, and leaves - a description applicable to a panda bear in a zoo in Oxford (See Oxford comma).
Eats shoots and leaves - applicable to a less well educated panda bear that has never been to Oxford.
With regard to your question:
- "Sit down, please, John!" - No - overly cluttered and difficult to read.
"Sit down please, John!" - probably a general comment to the room, with a forceful direct reference to John (Who is being especially disruptive...),from someone with some authority over John.
"Sit down, please John!" - probably a general statement to the room, but from someone with less authority over John (Pleading for him to comply).