It's good for out of combat shenanigans.
Such as moving potential enemies to dangerous areas (For example, when helping Karlach take out the paladins, you can use Minor Illusion on the wooden platform outside the rear door to make the shop keeper and ranger lass run out there and then you can enter Turn Based mode and use Thunderwave to send them both hurtling to their death. Thus allowing you to take on Mr Smites-a-lot on his own)
It can be used to aid with theft (Such as luring the Thiefling children away from their chest in the Grove so you can pick up the amulet to give back to the guy)
It can be a general use stealth aid to help an Assassin get a first strike off without the need of more limited Invisibility sources (Get people to turn around > Enter TB mode and walk your Assassin in for the attack)
You can sometimes group enemies up before initiating combat allowing you to get good AoE value at the start of a fight.
