There's a huge chunk of the fandom (I think) that isn't familiar enough with ACD canon to get that the episode title is a spoiler, so probably they needed the shot to get those viewers up to speed with the rest of us. It's a little gratuitous, but mostly, for me, as a viewer, it recements the way I'm feeling about Sherlock in that moment, stops all of my emotional energy from being drained away on John and keeps it tautly pulled between the two of them. Frankly, as weak as it is, it also keeps the episode from ending on the crushing note it would if it ended with John walking away from the grave--it's a signal that There Will Be More, you know.

This was my first post on Sherlock ever. My feels about Martin in that scene. I just can't.