Size matters, but it is not all about the size
If you are familiar with Docker, and have been using Docker for some time, you will probably already know or have read, that it is important and a good practice to reduce as much as you can the size of your images. Crafting your Dockerfile carefully to reduce the number of layers, using a minimalist base image to create small images, etc.
Sure, this is very important in order to save some space on disk. It will also reduce the network traffic, since at some point you will upload your image to some registry, to later download to a particular node or nodes. And sure, the startup time of your container could drastically be affected by bigger images, not because it really takes more time to spin up the container of a bigger image, but because if the image is not cached locally, it will need to be downloaded.