Recording real-world data may be cheap (not "free") in some circumstances, but properly labeling real-world data so it will be useful can be incredibly expensiv

Recording real-world data may be cheap (not "free") in some circumstances, but properly labeling real-world data so it will be useful can be incredibly expensive. Even if you're doing completely unsupervised learning, you will still need correctly labeled data at some point to validate your model. And - I tell you as someone who has actually tried to do this - getting a wide range of high-quality voice recordings across multiple speakers is NOT CHEAP, and trying to train a model that will work under real-world conditions using "whatever dataset I downloaded from kaggle.com" is a fool's errand.