Two of my stories in progress are planning to use this - technically, the latter is using three lines.
The first follows a special ops Rag Tag Bunch Of Misfits
sent into the heart of a zombie infestation to investigate several companies that might have accidentally or purposefully caused the entire mess, and to rescue any subjects of interest. The second thread follows a US Marine officer leading a detachment of (obviously) US Marines as part of a giant UN taskforce sent to deal with the zombies. The writing style and pace for both are different - the first line is more Left 4 Dead
, the second, more World War Z
The problem is, my early draft was criticized for not making it clear whenever the narrative would switch (even though they were always preceded by spaces in between paragraphs and establishing who was being focused on within the first few lines), and switching between action-heavy sequences, even if both narratives are dealing with combat, has been something that's always irked me about modern combat stories.
The second is a script of three different narratives during a very alternate World War II
. The first focuses on a normal Canadian Army captain placed in charge of an unholy mess of mercenaries, special forces, corporate soldiers, resistance fighters, spies, and regular troopers in the midst of World War II
. The second followed a US Army sergeant on the frontlines, who would often get entangled with the first group's antics, much to his misfortune. The third followed a Waffen-SS officer in charge of a coalition unit consisting of German, Japanese, Italian, and Spanish soldiers, made to prove to the Axis populace that We ARE Struggling Together
It's a script, so the differences are a lot more workable, but there's one large problem - the first narrative was very anime-like, with bizarre characters and weapons out the wazoo (someone uses a chainsword, even), the second was a general subversion of the typical "War Is Hell
and everyone is a psycho" war movie, and the third was a deconstruction of Alternate History
and to humanize the Axis a bit.