Unsafe Mimetypes allows a WordPress admin to decide which file formats can be uploaded to the media library
This is the error message you will see from the media manager when trying to upload many non-standard filetypes.
This is the admin interface where you can define a list of file extensions you wish to add to the whitelist. If you trust your editors you can also choose to grant the same permissions to them also.
If you want, you can allow your editor permission to upload the default types, while allowing your admins greater power by ticking the 'allow default types' box, and giving the extra permissions to admin only.