Relative performance impact of contexts

In best practices, Microsoft suggests the following for improved performance:

  • If you have only one instance per volume, use an instance context instead of a volume context
  • Save a reference to your instance context in your file, stream, or stream handle context (if you use it frequently I assume)

I have followed these recommendations, but I would feel better if I knew the basis for them. Are these recommendations just based on how many contexts need to be acquired and released, or is a stream context less work to retrieve than an instance context, and an instance context less work than a volume context?

_Ron