You can use semi-supervised learning techniques when only a small portion of your data is labeled and determining true labels for the rest of the data is expensive. Rather than using a supervised learning method to train a classifier on the labeled data and predict labels for the unlabeled data, you can leverage semi-supervised learning methods to fit labels to the unlabeled data.

If you want to predict labels for new data, you can use the predict object function of the semi-supervised classifier trained on both the labeled and unlabeled data.