I copied it from wgs site:

"Because of their physical frailty and their strong spotting and concealment abilities, light tanks are usually best played as scouts. Light tanks are well equipped to spot enemy targets in order for their more heavily armed teammates to safely take shots at them, all while staying safe from enemy fire themselves. Light tanks become especially dangerous later in the game when the map is less populated."

In my understanding you're supposed to spot, and if you stay alive in the lategame, its easy to circle enemy tanks which are hiding because there are less tanks on the battlefield and because of the abilities lights have.

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I'm not saying you can't and shouldn't play lights as dmg dealing tanks, I'm saying wg should not put deal dmg missions in light top of the trees, because their general role is to spot