We use it for various small tightly contained tasks in response to events (Kinesis events, S3 writes, etc), similar to how you might use Celery tasks to do some

We use it for various small tightly contained tasks in response to events (Kinesis events, S3 writes, etc), similar to how you might use Celery tasks to do something where either don't care about the result or the result might take to long to compute for you wait. As a completely made up arbitrary example say you send two types of emails to your users, a newsletter and personal notifications. You send the notifications yourself but have a third party service for the newsletter. When a user opts out of all emails you can make the required changes on your end but calling out to the other service might take longer than you are are willing to make a user wait. So instead you write something to S3 or Kinesis or some other stream that Lambda can access that takes the user ID and informs your email provider to no longer send emails to this address.