Once your company is notified of the pending case, a Litigation Hold may be called for the preservation of relevant ESI. If you have a properly documented retention policy where ESI may be destroyed in an automated (or manual) fashion, a litigation hold may force you to alter your process to ensure relevant ESI is not destroyed or altered.
Be aware that if data is not destroyed during “normal” business operations and still exists when entering into litigation (for example a “one-time backup” or old email archive you forgot to delete), they will need to be retained. Destroying them after you are notified of pending litigation in hopes of “catching up” with your retention policy can be seen as you trying to destroy relevant evidence.