In 2017, Ken Schwaber and I made the three questions in the Daily Scrum optional because we saw too many "zombie" teams that were giving lip service to the questions - not collaborating, not replanning, not swarming, and not removing impediments.
Also, we saw backlog driven approaches that worked extremely well. For example, in the "Shock Therapy" paper only one question is asked in the Daily Scrum. "Why is the top story not finished already?" And "How can every person on the team help finish it today?"
Nevertheless, the three Daily Scrum questions can be extremely effective if they lead to more collaboration and swarming coming out of the Daily Scrum.
What did you do yesterday?
A huge accelerator in a Scrum occurs when every developer sees the entire progress of the project every day. Hyperproductivity ensues when the typical comment becomes, "Wow, I thought it was going to take 3 days to do my next task, but I see from what you did yesterday that 3 lines of code and one hour are all that is necessary!"
This question tests the focus of the team. Anything done that was not work on the backlog is questioned. Meetings that are interfering with the Scrum are reduced or eliminated. Participants who repeatedly do not work on the backlog may be removed from the Scrum.
It also generates peer pressure to get stuff done that is impeding the progress of others.
The Scrum Master wants to know what tasks are "done" and whether tasks in progress will complete as expected. If estimates are expanding or new tasks are discovered, this will change the burndown chart.
The Scrum Master also wants to minimize work in progress. Too many open tasks at once introduces risk into the Sprint and is an early warning that delays may be expected.
What will you do today?
This question replaces GANTT charts. Dependencies are constantly changing. Answering this question revises project strategy on a daily basis by reorienting the team due to dependency changes that were revealed by the previous question.
The question also surfaces dependencies or tasks that may have been overlooked. This will revise the plan in the minds of the team.
It also tests the focus of the team. Anything to be done that does not further progress is questioned.
The Scrum Master wants to know what new tasks are starting. Failure to see tasks opening and closing regularly is an early warning that things may be going off track.
What is blocking progress?
Impediments to progress are often caused by software or technology not showing up at the right time. The Scrum Master or the team may be able to resolve this. Otherwise, management must fix it.
Blocks are often due to meetings irrelevant to the SCRUM. Often management must get involved to fix this. In the early days of Scrum when Ken Schwaber was acting as Scrum Master he would tell team members not to go to any meetings except Scrum events. Whoever complained would have to talk with Ken. A great Scrum Master knows how to deal with management.
Hard technical problems often slow things down. The team can often fix this. Alternatively, these problems may be escalated to bring in other resources.
This question will create issues that may result in new stories in the Sprint Backlog. It could revise the plan.
The most important effect of this question is to create a list of impediments that are assigned to the team or escalated. A major responsibility of the Scrum Master is to manage, prioritize, and assure this impediment backlog is burned down. The Scrum teams should expect management to help work the impediment backlog. Eliminating bottlenecks is the fastest way to improve productivity. See Goldratt's book, "The Goal." All managers should read this book. Developers will find it useful also.
One of the biggest impediments to improving productivity in Scrum teams that I see in many companies is the failure of the Scrum Master to track and prioritize impediments. Management cannot help fix them if they are not clearly identified along with a recommended plan of action.