Rector works with all class names as fully qualified by default, so it knows the exact types. In most coding standard, that's not desired behavior, because short version with `use` statement is preferred:
If you have set `Option::AUTO_IMPORT_NAMES` to `true`, rector is applying this to every analyzed file, even if no real change by a rector was applied to the file.
The reason is that a so-called post-rector is responsible for this, namely the `NameImportingPostRector`.
To remove imports, use [ECS](https://github.com/symplify/easy-coding-standard) with [`NoUnusedImportsFixer`](https://github.com/FriendsOfPHP/PHP-CS-Fixer/blob/2.18/doc/rules/import/no_unused_imports.rst) rule: