What does zwift ask “what was your max heart rate”?

Hi all, I’m doing the 4wk FTP builder training and was wondering about some of the messages that zwift shows while riding.

In particular I was wondering why during the 40/20’s session it asks what my max heart rate was during the session. Obviously zwift knows, so what does it mean if my heart rate is higher / lower / same in each of the efforts?

Thanks!