When a package is smashed, all of its symbols are uninterned, and the package structure is deleted. Also, its function definitions, property lists, classes, values, and structure definitions are deleted or set to
See Smashing packages for more details.
CAUTION: Smashing destroys a whole package and all information within its symbols. You are advised to avoid using it if possible. A better alternative, if you cannot deal individually with symbols, is :smash-packages-symbols.