It has to do with Kharkiv.
Launching an advance that far (some suggested they make 20km into Russia, that would mean they make more progress in Russia in 1 day than the Russian made in Ukraine in the last 2 months). Means only 2 things. Either
1.) Ukraine is doing a massive Brigade size Recon-in-Force
2.) Ukraine is aiming to break off Russian troop build-up in the region since May as reported.
If it was 1. Then their ultimate goal is to harass the Russian troop and try to determine their troop strength in the area, and gain more intel, something very specific to have launch an recon-in-force like that.
If it was 2. Then it basically a security operation, where they went in and clear some Russian defence pocket, stop them from getting into formation to attack Sumy or to interdict manpower or supplies into Kharkiv offensive.
But some analyst suggesting they are taking those town (They took Sudzha at least) in order to trade them with Russia, that's very unlikely.
