These are not integrated into the narrative. They're metagame justifications.
Unless the narrative includes the DM as a character unto themselves.
The narrative emerges from the game play.
I do not play NPCs in the party. It is a sure way to get to lose objectivity. I let the players play their henchmen (sidekicks) whenever they have one. And yes, they do tend to have a few. As henchmen often become the next character when one dies.
Also. Random encounters forces a DM to improvise the results, integrate them into the narrative and often find justifications for the presence of said monsters/foes/events. Heck, players will often find better justifications for the presence of a monster than myself.
Random encounters prevent a few things such as:
1) It prevents the DM to "Tell" a story in which the characters have no say in the story. They are the actors in the DMs' story. For that alone, they are worth it.
2) It keeps the players on their toes. When resting is just a simple matter, it removes a lot of the tension of invading a lair.
3) It makes the world much more believable. Yes, the story is centered on the players, but the world isn't. Things continue to happen while the characters are doing something else.
4) It also pushes players forward. I use random encounters to push the 6-8 encounters per day. I create my own tables fitted with the current adventure, area or campaign in mind with a possibility for "general" unrelated encounters. Not all encounters are hostile in nature.
5) Since random encounters do not give treasure and/or experience, players will tend to find other ways to resolve them whenever possible. They do count for the 6-8 encounters period however and using a short rest (a day in my campaign) means that this rest must be carefully considered.