The Ukraine war has already been fantastically profitable for Putin for one immutable reason: a blooded army is vastly more effective than a body of naive recruits. It's not even close. Ukies, unlike Arabs, can actually fight back. The war is real enough as far as Putin's soldiers are concerned.
One of the things your soldiers need experience doing is shooting down trespassing aircraft. Can't practice that if the other side can't launch any aircraft.
Plus it's a great way to destroy Ukrainian materiel. How can you be sure you got all their planes? How do you know you didn't only hit tarmac and they can't launch? Simple. Let them launch (in low numbers) and then shoot them all down. Admittedly I'm not 100% sure this is strategically relevant, but if it's something you wanted to do, that's how you would go about it.
Come to think, you might want to do this precisely if you don't intend to hold the territory. Sure you might ask them to destroy all their war materiel in surrender talks, but unless you occupy the place there's no way to ensure they actually do it. Plus they may pull a Weimar/Japan and simply go back on their word later. "Loan" the planes to NATO so they're out of the country, then NATO "pay" the planes back one day when Putin isn't looking. Can't do that if all the planes are in 1000 pieces by the side of the road.