This will pave the way for the Russians to release Iranian property (purchased S-300 batteries) which they have been keeping hostage for a few years.
If the Russian's are smart, they will release the Iranian S-300 batteries to Iran. Afterwards they can claim that since Iran already possessed a similar system, this transfer did not significantly shift the balance of power in the region.
"The world is a dangerous place. Not because of the people who are evil; but because of the people who don't do anything about it."