This isn't an area I'm super well versed on but I can give a cursory explanation until someone with real credentials shows up:

War elephants were used most often as walking tanks, smashing through infantry and occasionally cavalry and leading to routs and at the very least a huge loss in moral. Their presence on the field were huge boosts to friendly troops who would see those beasts charge headlong into the center of the enemy formation causing chaos. Then friendly infantry or cavalry would then exploit those openings.

The risk came if/when the elephants got out of control and rampaged, as then they could do a lot of damage to friendly troops, throwing them into a rout instead of the enemy, which is why it was always important for generals in command of elephants to not expose them to skirmishing troops like javelin throwers or archers, as the rain of missiles could cause the animals to become uncontrollable.

I suppose that elephants could have been used to guard key locations at least from cavalry charges as horses would undoubtedly avoid them, and if the army was using towers on the elephants then the structures would have been perfect for picking off enemy troops below. I can't say more unfortunately.