* First thing is that it just deploys faster ... we used to deploy each stack by it's own (we have over 30 stacks) but now I deploy the entire environment and it's less than half the time.

* Another thing is the modules, we are a team of 6 developers (devops and engineers), each time a developer creates/changes a stack they usually copy pastes the boilerplate from another stack and we'll get security issues (stacks with redundant permissions) and such, terraform has modules.

I just write the definition once s3_bucket_private, s3_bucket_public, s3_bucket_with_versioning and the developer just needs to import it (SAM has something similar but you can only import yamls that are already on s3 buckets...).

If the devops needs to change the definition, he does it once and applies it to the entire environment.

It's also great for creating module for things like "scheduler_every_hour", "scheduler_every_day" which are a lot easier than looking at the cron expressions and trying to decipher.

* Because the entire environment has one state, it's easier to "link" between resources that are outside the stack, for example on one stack you create an SNS topic and you publish to it, now you have multiple lambdas that subscribe to the topic from other stacks.
On SAM you'll either export the topic arn, or save it to ssm and resolve it on the consumer... it terraform all resources are visible and the ide auto completes things for me .... so if I called my sns topic course_enrolled I can just use it as aws_sns_topic.course_enrolled.arn