Thank you very much for explanation.
Now after I know that «hide weekends» doesn’t mean (anymore) that weekends are hidden in the burndown, I understand the line.
Still, if I don’t hide weekends, the line is straight, which means it is expected that the team will work on weekends.
So I summarize my understanding:
1. the burndown always includes weekend days (x-axis)
2. «hide weekends» means: «team is not expected to work on weekends» -> ideal line shows flats
3. don’t «hide weekends» means: «team is expected to work on weekends» -> ideal line doesn’t show flats
Right?
BTW, I cannot exactly see the benefit you explained «A benefit is …, while flats in your curve in other places means that there is probably a problem» since in the past a flat in the burndown always indicated a possible problem. Well, now I know again how to read it in icescrum.