TL;DR

Mounting a Kubernetes ConfigMap as a volume in a Pod might enable getting updates as the ConfigMap is changed. With some exceptions.

To make a long story short:

• what you find in ConfigMap is mostly true: mounting it as a volume will give you the benefits of having updated stuff when you change the contents of the ConfigMap;
• when you use subPath to mount a file in a specific location, though, another piece of documentation clarifies that:

A container using a ConfigMap as a subPath volume will not receive ConfigMap updates.

So… you have been warned, future me!