You can choose to set the privacy of each gallery to "Public" or "Private" in Gallery Settings.
For public galleries: Client can simply share their URL with anyone else. As it's an unlisted URL, only people with the link can view.
For private galleries: Private galleries have a built-in sharing option, and clients can easily send a private invite to their friends/family to access their video or album. Each shared recipient also receives a unique access code. Client always stays in control of the privacy, and can also revoke access. You can also choose to disable the share button.