Why does Android have 2 fonts at the same time?

As a very relatable example, we have Android OS (since which version I do not remember) using 2 fonts, one for headlines and one for the rest of the text.

As in the image, we can see that it uses 2 fonts. Noto for Headlines and Source Sans for body text. By default, I think the combination is Circular+Roboto.

So, Generally, the question can be rephrased as:

" What are the pros and cons of using 2 fonts on a single page/throughout the app".