I can see tactics using the obsolete tanks that would advantage Russian efforts. Similar to the cannon fodder, human bait tactic they are using to identify and target Ukranian positions, they could use the obsolete tanks to draw fire from weapons like Javelin or other portable anti-tank weapons. Even if it does not provide targeting info for Russian artillery, the trade of an obsolete tank for the expenditure of a quarter million-dollar missile, seems to favor Russia. Also these obsolete tanks can function like self-propelled artillery and never need to fight face to face with other tanks and let them burn up ancient ammo not really fit for tank battles.