Small images are useful in many scenarios. Developers iterating locally don't have to wait as long to produce them, when you deploy them to many machines, you don't have to worry about as much bandwidth due to the thundering herd problem, and you're paying less for storage for your docker registry, this all adds up. I've got thousands of docker images in my registry currently, which is SaaS Artifactory, and the transfer and storage costs are significant.

A tiny image for running your app, such as an Alpine Linux base with a static executable in it, is also much more secure since your attack surface is significantly smaller.