You can define your whole cloud infra as code so you don't have to manually maintain hundreds, sometimes thousands of resources manually. My work would be basically impossible without it, or the DevOps team shouldn't consist of 5 peope but 20. It's a descriptive language where you define the end result you want to see and Terraform transforms your code to actual API calls to AWS/GCP/Azure. Like this

resource database MyAwesomeDB {
engine = mssql
version = 1.1
backup, initial db, master pw etcetc. }

It's incredible useful where you have 50+ microservices, 10+ db instances, load balancers, gateways, auto scaling rules, object storage, nosql, queues, countless firewall and routing rules, notifications and observability systems. And that was just dev. Then you have test, staging, prod, plus multi-region on top of that. And of course ephemeral environments fired up for every PR so the dev can test their shit without messing everything up. You end up easily managing a couple of thousands of cloud resources.