Like Jay, I think that it is unimportant what this might be called. I agree with him that the reader should understand what is going on. But to me, much more important is the question wether your readers will want to follow you along that detour.
Every reader loves a straight story (if it is well told). I have never read a review that complained that there where too few side stories or too few parallel storylines or too few tales told around the campfire. No one is unhappy about a story that sticks with one protagonist and follows him or her to the end.
But I personally dislike parallel storylines. I have written elsewhere in another answer that I get thrown out of the story whenever George R. R. Martin switches to another character in The Song of Ice and Fire, and it feels like I really don't care for the next chapter's character and have a hard time getting back in – only to be thrown out again at the next chapter end.
When I read, I identify with the protagonist. I care for what he or she cares for. I am the protagonist, and I want to have things happening and to get to my goal. I don't care about all the tales that my companions tell around the campfire and that some authors make to last chapters, while the enemy is making ready to fall on us. I don't care about what my best friend goes through when the last thing I know is the cliffhanger of some assassin jumping me.
Do you see what I mean? I – for as a reader I am the protagonist – am in the middle of the most exciting or frightening action, and I don't want the author to push the pause button and tell me things that might be interesting at another time but feel completely irrelevant when I'm about to be die, make love, or whatever.
And I am not the only one. While no one complains of an author sticking with his protagonist, many readers are like me and are thrown out of the story by these crass changes in viewpoint and storyline. You can read it in countless reviews. When you chose to switch, you will lose some readers. How many, will depend on your mastery. I did read GRRM's novels, because they are just so masterfully told, but I did not enjoy it as much as some other books. I was bored by the ents in the Lord of the Rings, but I did read that chapter, too, eventually (although not the first time around).
So I did pay for those books, and would do so again, but only because those are masterworks.
Can you grab me – and the others like me – enough for me to buy another book by you once I was disappointed by your first?