When and how to avoid using nodes for everything
Nodes are cheap to produce, but even they have their limits. A project may have tens of thousands of nodes all doing things. The more complex their behavior though, the larger the strain each one adds to a project's performance.
Godot provides more lightweight objects for creating APIs which nodes use. Be sure to keep these in mind as options when designing how you wish to build your project's features.
Object
RefCounted
Resource