I'll take the Canadian Army as an example: At first, we only had troops over there (Afghanistan). Then, we wanted a something that would really make the war VERY unfair. The something was: Leopards C2! It was pretty much something to set us apart from the enemy who relied only on Guerrila Infantry (apart from IEDs, damn IEDs...). If your enemy doesn't have tanks, get some and watch them struggle to take them out. If your enemy has them, get better ones (it was either the first or second Gulph War where the American's destroyed all of Sadam's petty Russian tanks without loosing one).
Tanks are useful in urban combat situations believe it or not. If you look at videos on Youtube, pesky insurgent snipers in Iraq have been made short work of with the Abrams' Cannon. The ability of laying down a very large amount of firepower (one you would find on an Abrams' tank: .50 cal, 7.62, and another 7.62 co-axial) will very easily turn the tide of battle.
Tanks in an open environment? Even better.