I received free sessions for maybe a year and a half from my longtime T. Once I turned 18, she didn't want me worrying about my parents being in any way involved (by paying). Once I got a job, I started paying her a very reduced rate. I felt very appreciative of her doing that for me. As for if I felt like I owed her... I'm not sure. I guess I did/do, but not in a way where I feel like I need to make it up to her in a tangible sort of way. It's hard to explain.

Edit: That said, I've never felt entitled to free sessions. I really respect my T's time and she deserves to be compensated.