Reflecting on the relevance to the rest of the story I agree with Kazza 474 that Sherlock’s “being bored† is the main purpose for this scene. It goes as far as to shoot the wall and even a journey to Belarus isn’t something that seems to stand out of his everyday life.
I also found two little references during TGG:
Sherlock’s “open and shut DOMESTIC murder – not worth my time!† seems funnily to correspond to Mrs. Hudson’s “You two had a little DOMESTIC?†. (I don’t remember the word “domestic† elsewhere in the series.) And Mr. Bewick’s insistence: “It was an accident, I swear!† is later repeated by Joe Harrison when Sherlock and John confront him with his killing of Westie.

If you listen to the commentary that goes with this episode the writers basically admit that the whole scene is set up as something of a joke because the whole thing is just a lesson in grammar.

"without you I'll get hung for this'
'No, no not at all. Hanged, yes'

Basically 'things' are hung; people are 'hanged'.

I love the Grammar Nazi reference, it's so 'OCD' (similar to the sock index really) and very fitting with his character.

Hmmm--  I  wondered about the minsk belarus scene too.   I still think Sherlock went there because the cops there weren't getting anything out of the prisoner.   

I  have read all  of the canon stories,  a long time ago,  and...could  this be one of the stories that Holmes referred to,  but that was never written up,  by  John watson?  Holmes made MANY references to other cases which we don't know about.   Doyle  put those in, to illustrate a point,  OR  to throw us off track altogether.   that being said,  maybe the writers just threw that scene in there,  to add more time to the 90 minute film.