The Scaled Agile Framework calls for teams that are stable and long-lived. The operating mental model is that teams need to be carefully designed up-front and are a static group of individuals. The underlying thinking is that (1) there is a cost to moving teams through the stages of the Tuckman model (forming, storming, norming, and performing) and it makes little sense to keep incurring this cost when teams are continually formed and disbanded for each project, and (2) it is easier to get to a place of predictability when team members can practice interacting successfully and efficiently over a period of time — i.e, gelling together.
However, there is an equally valid and completely different way of looking at the situation. There are numerous situations where people who haven’t worked together previously can be highly productive right from the start. Company hackathons where people from disparate areas of the organization come together to work on a problem for a few days exhibit teamwork on the fly and can solve problems that long-standing teams struggle to. The same holds true for what happens in emergency rooms where staffing changes every shift, and in product innovation (e.g., Honda City development).
Where the situation is complex or when it is unclear how to obtain the desired results (disruptive or Big I innovation) it may be better to have teams whose composition can change at any given moment — new people with the required expertise are added to these porous teams. It is also appropriate to have ambassadors from other teams join a team of experts for a brief period (3-4 weeks) to learn and then take back the information and behaviors to their respective teams.
What stands out in the fluid team approach is the high degree of passion, non-coercion — an attitude of “I really want to be here doing what I’m doing,” saying what needs to be said, collaboration, rapid learning cycles, competence, performance improvement initiative, and clarity of outcomes desires.
In summary, for routine processes stable, long-lived teams can work well. In more complex and uncertain environments, dynamically constituted teams might be a better approach.