An agile team should be made up of committed individuals whose focus is solely with the team.
This is well understood to be a core tenet of taking an agile approach to software development (though this also applies regardless of development methodology).
Why is it Important?
Tuckman's stages of group development, proposed back in 1965, suggests that new teams go through 4 stages: Forming, storming, norming and performing.
This model describes how a team takes time to truly gel, going through the stages of initially getting to know each other, gaining each others trust, resolving any personality clashes through the pursuit of a common goal, and finally ending with the motivation and knowledge to perform at a high level.
Changing the makeup of the team with even a single person can throw out the dynamic of the entire team, resetting this process back to 'forming'. It's important that a team is given the time to properly coalesce and enter the 'performing' stage.
The Impact of Change
When resetting the group dynamics, expect to see impact in some of the following ways:
- Ownership: when a team has a sense of ownership of their work, they will be more engaged and committed to achieving great things. Who is responsible if people are coming and going?
- Trust: this takes time to build. Once a team trusts each other is doing the right thing, they will often go the extra mile for each other.
- Motivation: it can be a real motivation killer when conditions are changing constantly. "Why is bob moving to project Y, we had just formed a good working partnership?"
So Never Change?
That's not to say that change should never be permitted.
Change will happen (it's the only certainty in life after all), but it must be entered into with the understanding that it will have a sizeable impact on performance, and potentially start down a road towards more upheaval.