Yamato explains the goal is to capture Sasori's spy, which could lead them to Orochimaru and, ultimately, Sasuke.
"The Scroll's Secret: No Peeking Allowed" Arc: Chūnin Exams (Forest of Death) Naruto Episode 35
"An Unnecessary Addition" Arc: Tenchi Bridge Reconnaissance Mission Yamato explains the goal is to capture Sasori's