1st, its HVAR, not HAVAR.
2nd, they were not efficient to take on the tanks other AFVs directly, since the accuracy was pathetic (about 1 out of 20-50 projectiles would actually manage to hit a tank, while aircraft cannons were 10-fold more accurate).
BUT (and a big 'but'), since tanks have a large logistical footprint, the destroying of fuel ammo trucks, repair shops etc. would've render tanks almost immobile.
One other thing is that tank crews under constant threat from air would've been buttoned-up almost always, furthermore hampering their performance.