What useful applications can PyTorch make?

Honestly quite a lot. Pytorch is a framework just like its counterpart: tensorflow. May I suggest googling something like “text prediction/classification using torch” as an example. Better yet: find a github repo with a train/test dataset and see if you can replicate and improve models and scripts.

One library built on top of pytorch is “flair nlp”. Have a look at their repo for examples of how useful their application is.