Naruto creator Masashi Kishimoto does a decent job allowing other characters than the titular Naruto to take the forefront through their fights. These battles highlight the depth of side characters and give the sense that its world is moving and changing, even when the protagonist is not around. When Sasuke fights Deidara, for example, the former is still in the midst of his antagonist arc, so their bout adds weight and depth to the two antagonistic forces doing solid footwork for the Akatsuki -- and Sasuke continuing to plunge into darkness.
After Deidara gets overwhelmed by Itachi Uchiha's Sharingan, he commits to perfecting his ninja arts to overcome the Uchiha clan's overpowered ability. Crossing paths with Sasuke gives Deidara the convenient opportunity to prove his art against the Sharingan while avoiding any Akatsuki infighting. Not one to run from any battles, Deidara explosively initiates this clash, only to see his attempts at overcoming Sasuke prevented by the latter's willingness to sacrifice others.
Sasuke's reaction to Deidara's initial attack calls attention to his mindset: he is willing to sacrifice whatever is necessary to obtain his goal of killing Itachi. Sasuke's cold and calculating side allows him to utilize the elemental system of chakra at a level rarely seen in Naruto. Using his sword, lightning chakra and cursed mark, he can thwart most of Deidara's arsenal.
Deducing how to defuse Deidara's explosives by using his lightning skills during combat reveals Sasuke's growing battle acumen. This skill contrast manifests through the scale of destruction caused by Deidara's artful earth-based attacks and Sasuke's concise sword and lightning-based moves. It makes for an exhilarating display of the varied styles of combat and chakra in the world of Naruto.
Sasuke and Deidara's battle causes them to run the full gamut of their abilities. Deidara's explosive art has a complex array of uses that cause Sasuke to tap deep into his skill set to survive the incendiary battlefield. This display of abilities clearly shows the Akatsuki's potential power as their youngest member pushes a Sharingan-equipped Uchiha who trained with Kakashi and Orochimaru to the limit. However, Deidara's desire for victory leads to his loss as he doesn't account for Sasuke's drive to survive.
Coincidentally, both Deidara and Sasuke shared a similar goal of defeating Itachi and proving their strength. Deidara entered the brawl with a sense of superiority, viewing Sasuke as proof of his own growing potential and ability to overcome a Sharingan. Instead of overcoming an Uchiha, Deidara ends up acting as an educational threshold for Sasuke by driving him to extremes to survive. Sasuke's willing sacrifice of Manda to endure Deidara's grandest scale explosive is a peak moment for his antagonistic arc.
Deidara's human desire to prove his art and strength against a powerful rival highlights the depth of individual members of the Akatsuki. His humanity also builds them up as a complex villain group whose members are willing to break from the team's goals to follow their own dreams.
Displaying the growing hostility of Sasuke's vengeful mindset during this fight leads satisfactorily to his inevitable conflict with Itachi. Naruto's progression for characters and groups that are not the lead protagonist spotlights the importance of pushing the secondary protagonists or temporary antagonists into the forefront.