It works for several reasons as we saw Sat. night:
1) It's very hard for lines to consistently dictate play and outscore opposition. Especially for lines that will face top opposition every night. More often than not, individual players can't themselves push the meter on these things much. There are definitely exceptions, but they are very few and far between. The concern is that if you load up a top line then if and when that line struggles or gets shut down, you have nothing behind it to attack with. But putting your best players together makes it exponentially easier on each of those players not to be shut down.
Nobody would look at Boston or Colorado and think that Bergeron, Marchand, Pastrnak, MacKinnon, Rantanen, or Landeskog aren't good enough players on their own to play on their own lines. But it's undeniable that when these players play together they open up so much for each other and are so much harder to defend individually for the opposing team. Two teams off the top of my head that notbaly made this switch this year and teamwide have had phenomenal success for doing so are Calgary and Nashville.
2) We've spent so much of the last two seasons trying to find the right RW for Strome and Panarin. What is the value of their chemistry to the team if it is predicated on a third player that also matches that chemistry more or less perfectly? Ultimately, what we've seen is that Panarin and Strome don't necessarily make each other better; Panarin, Strome, and Jesper Fast was a dominant line.
3) Strome has proven himself to be a capable top six center. He doesn't need Panarin on his line. He's also had great results with Lafreniere across the last two years.
So, on this team it has a lot of value for pretty simple reasons. It allows the team at large to play the kind of N-S, four line hockey Gallant wants, while also creating a situation that can still maximally leverage the skillsets of the teams two most talented players, Zibanejad and Panarin. It solves the problem of LW/RW slotting in the top six (which was always ridiculous). It frees us from the self-inflicted problem of the right right wing for Panarin-Strome. And it better allows for the youth/talent to mix with the veteran/grit in the middle six.