Once upon a time, we used to have lambda functions with deployment packages reach 50MiB. We tended to test locally, zip all dependencies, and wait until it became available for testing after uploading the files. What makes it worse is when we have bad internet. Fortunately, now we have Layers!!
What are Lambda Layers?
In short, Lambda Layers is an approach that makes appending extra code to a Lambda function easier. It keeps the development package smaller and easy to maintain.