One is to clear the territory. But even that was a side benefit.
When you have a "tribe" that's wedded to the land and fights as a unit, you dissolve the unit. Remove it from the land. They have less to fight for, and they're distributed. The Circassians were split up from the Caucasus by the Ottomans for this reason. Stalin did it, but he learned it from history--the Horde and the Ottomans did precisely the same thing.
Stalin moved the Tatars, not to relocate Russians in their place (even if that happened) but for the same reason FDR put West Coast) but not East Coast Japanese(-Americans) in camps. Get unreliable elements away from the front line. The Turks did something similar with Kurds and Syriac Xians.
In this case they also might be intending to use them as a kind of hostage in negotiations later.
It's also possible that Putin's going full-tilt abusive big brother. "I can't let the Russians stay. They'd be assimilated, and that's genocide! So we'll force them to stay Russian to preserve their cultural-ethnic purity." Remember--genocide of Russophones is one of the reasons given for this "special operation".
But I wouldn't rule out that he just wants a photo op. "Look at the grateful people. Yes, that's the Ukrainian hand gesture for 'we're #1!'" Or justification for the numbers--all the evacuees from Khar'kov, Mariupol have wanted (or at least 99% of them) to go back to that muthuh, Russia. At some point you need to have actual people to justify the 10s of thousands of those personally saved by their messiah Putin.
= new reply since forum marked as read