"Well. I get enough practice fighting with being Ladybug. But I guess it couldn't hurt to train outside of being transformed. Just in case."

Because she never knew when things might get dangerous. And she often wasn't already transformed until after she knew there was someone running around with their akumatized state. So it was probably a good idea to try and train a little more as Marinette. Just in case she found herself needing to deal with things until she had a chance to transform.