What is the difference between Copy / Reference when inserting a Snippet?

When inserting a Snippet, you have two options: Copy and Reference.

Copy means that the inserted Snippet will be available to edit in the campaign or template on-demand.

Reference means that the inserted Snippet will reference the original file in the Snippet library, and cannot be edited at that time.

Snippets pulled into email templates will be reference only while Snippets used in campaigns can be reference or copy.