Gem Layer
Jets bundles your project’s gem dependencies in a Gem Layer which is a Lambda Layer. From the AWS Docs:
With layers, you can use libraries in your function without needing to include them in your deployment package.
Advantage of Gem Layer
An advantage is that it results in your code size being smaller. If your application code is under the key 3 MB limit, you are able to see and edit your Lambda code in the AWS Lambda console code editor live. This is helpful to debug and test without a full deploy. This only works with config.package_type = "zip".