I agree with this! Personally, I have a CS degree and a PhD degree in Natural Language Processing, although my current interests are larger than this. For instance, I work as web developer, do some mobile apps, do data processing and some tutoring, as they traverse a big range of my current interests.

Later on you can start mixing things. For instance, I do freelance tutoring on these subjects, I use my webapp backend Python code on an Android app I have, etc..