Bad style to start text in subsection?

I asked my supervisor the exact same question while writing my master thesis. He said that it is a matter of style, he preferred putting an introductory text under each heading. I looked over some articles in my field as well, and they were pretty divided on it.

If you have a style guide from your university/publisher, or if you have examples available, I would say, follow those. Otherwise it's up to you.

I found it good practice, because those are the places where you write a short summary/introduction for that chapter, which could help you organize your thoughts.