Thought I would expand upon some of the other answers here. Personally I think that adding to an active sprint is a very bad idea.
Scrum is all about the team committing to finish a scope of work that is set in stone. The team commits to that work in the planning before the sprint begins.
During the sprint, the team should be kept distraction free to focus entirely on implementing their commitment.
For those who disagree, has one read the original Jeff Sutherland Scrum bible?
With this in mind, let’s review why adding to the sprint might be a bad idea.
Firstly, it encourages individuals to increase scope without first consulting the team as a whole.
Everyone took part in planning and committed to the work. This takes a lot of time and effort. So, similarly, adding any additional work means that the team should review this and commit.
This is obviously hassle during the sprint. Individuals consult the product owner and discussions ensue. Perhaps there are several candidates to add as the backlog is not quite ready. After all, it doesn’t need to be ready as there’s an active sprint in progress and this was unexpected.
Disagreements about what to add and priorities of non sprint work then becomes a major distraction.
OK what about if all work is finished?
In my lifetime in working in Scrum, I can honestly say I’ve never heard a question about adding to the sprint, opened the Scrum board, and seen a board with all work done. It’s always a busy board with lots of work in progress!
What this question highlights are two things:
- the individual and possibly the team needs Scrum training
- the team has underlying issues
Typically the individual is not collaborating. They have finished their work and they are looking for a new individual task. This should not happen in Scrum if there is any unfinished tasks.
Instead, the individual should be collaborating with others, working as a team to finish each task in turn. That collaboration and teamwork is the essence of Scrum! An individual "running out of work” or “with nothing to do” should never happen. The Scrum team will run out of work when the sprint ends.
Temptation, temptation, temptation!
Because it’s a lot of bother to discuss what new work to add, and there exists a culture of adding more tasks to the sprint, it’s very tempting to simply drag new work in without consulting anyone.
This is a very dangerous practice. Perhaps the individual chats to the product owner, agrees some priority, adds the work and assigns to themselves.
It can be an unpleasant surprise for team mates to see the scope of work increase. The Scrum Master then faces additional headaches in “policing” the sprint backlog.
It Distorts The Burn Down Charts
The hint is in the name; Burn Down. That is down not up. The Burn Down chart should never burn up. If this chart is burning up then the Scrum team should carefully consider the issues presented above.
So, what’s the solution? Well thankfully there is a very simply and easy solution. That is, simply finish the sprint early! This avoids all the issues mentioned above. The team can review the early finish during the retrospective and commit to more story points in the subsequent sprint. Over time they will refine and at some point will finish on the final day as intended.
This will be much easier if they are distraction free to focus entirely on their commitment.
If in the early days of the Scrum team, they finish a few days early. So what? They still continue working and picking top priorities off the backlog. It’s not a problem to worry about because the team accuracy will increase and this problem will go away.
Teams that add to sprint backlogs, work individually and so on, really need to introspect. Do they consider themselves a Scrum team? What is a Scrum team? The answers maybe quite revealing. There may be confusion as to what is Scrum. Moreover it maybe that the team does not want to be a Scrum team once they really understand what that means. That’s ok! There are other approaches and some may work much better. It’s all good.