I think the argument that would be made is that it is being done for defensive purposes in the sense it's forcing the Russians to use reserves inside of Russia that they were intending to use in Ukraine at some point.
True.
There is some logic to that, but it seems doubtful that it will exhaust Russia's reserves enough to make it worth the costs to Ukraine.
Undoubtedly true. These maps make the point about how insignificant the Ukrainian incursion is compared to the ground they have already lost:
Yes, that tiny pocket is the Ukrainian advance.
It may end up leaving them even more vulnerable to a larger Russian offensive at some point.
Truth. This is Ukraine's Battle of the Bulge. They are looking to push far enough into Russia to force Russian troops out of Eastern Ukraine so they can try and get some sort of peace deal. The outcome is very likely the same.