Of what importance is the character of Horatio in the last scene of Act 5 of Hamlet?

In Shakespeare's Hamlet, Horatio is
the go-to guy throughout the play.  The guards go to him when they see a ghost.  Hamlet
confides to him his plans to fake madness.  Hamlet seeks his help with his plan to trap
the king during the production of the
"play-within-the-play." 

At the conclusion, Horatio is so
loyal that he is willing to commit suicide when his friend, Hamlet, is dying.  But
Hamlet stops him.  Horatio, always the trusted friend, must stay alive to tell the tale
of what really happened in Denmark.

Also, looking at the
situation practically, Horatio provides occasions for Hamlet to speak.  In other words,
since this is a drama and no narrator exists, dialogue is one of the methods used to
reveal plot, characterization, intentions, etc.  Practically speaking,  Horatio is
present in the final scene to give Hamlet someone to talk to, to give Hamlet someone to
reveal his thoughts to so the audience can hear them.