I think Ms. Claveau has identified the issue very well.
The example you gave was a very good one. Of course, we will never object to witnesses being spared having to travel when it is just a pro forma date and everyone knows the trial will be postponed. In that kind of situation, the lawyers will certainly work together and arrange with the court for those hearings to be held by videoconference.
However, where there are fundamental matters in issue, where there is testimony, where the presence of the accused is necessary, and where it is known that the trial will be held on a specific date, as Ms. Claveau said, then the parties can be alerted and it can be ensured that the proper procedure is followed.