There's an interesting theory somewhere that goes on about how the removal of these accessories represents her shedding the symbols of nationalistic bias and generalised society. The burnings could symbolise the difficult hurdles that she's overcoming in her efforts. Sakura isn't just another soldier in a coalition's joint military group - she's a person of independent interests who is pursuing her own goals of fighting and providing for her closest friends, her teammates, in a battle set apart in another world against another enemy than the one that the Alliance was fighting.
It's mostly conjecture, but I do like the concept of Sakura "transcending" the mundane duties of a simple soldier and distinctively acting in a battle against the extraordinary with extraordinary allies/her friends.
I would agree.... The changing of her outfit does signal a transformation. Or rather, it will signal it. We, the readers, see and understand why she had to shed her clothes. But when the fighting is over and she returns to liberate the rest of the shinobi, she impact will be felt. She will have transformed.
She didn't go down with the rest of the shinobi or med-nins, those that will still be walking around dressed in their vests and lab coats. She made a personal sacrifice to save the world, as shown physically by the torn clothes.
Kishimoto has been really big on showing characters, good and bad alike, losing parts of their clothing in the final showdown. It shows the seriousness of the battle and their commitment to win.
Sakura is not getting a dramatic outfit change like Sasuke and Naruto. Those were closely tied to their power-ups. However, Sakura's removal of her sleeve (and hopefully the other one too) showcases her new powers. She looks fierce with the purple bands wrapped down her arms. Which ultimately I think is the point of having that scene: to show off the extent of her powers. She's doing more, going farther than she has before.
And, at the risk of promoting SS handwringing, I'm sure that the last image of Sakura's vest left behind in the sand, with the Uzumaki symbol on it partly burned into, was latched onto as proof of the return of SS. That image would make good symbolism for a change in Sakura's storyline away from Naruto and back toward Sasuke. Lol - but as we know, Kishi is the ultimate troll, so I think it's just a two-fer with the imagery (Sakura sheds her appearance and SS scores a point).
Anyway, yeah, the use of clothing, or lack of it
, in this story shouldn't be overlooked. It almost always means something. And I agree it means moving Sakura away from the general ranks of the shinobi and into her status as a powerful individual and rightful member of the neo-Sannin.