There are four phases in team building: Forming (team is created), Storming (team debates and argues about what it needs to do), Norming (team agrees how it will work), and Performing (team starts to deliver). The first three phases are time consuming and during this period the team is rarely performing.
So intelligent managers try to ensure that they minimize the amount of team creation they have to undertake. Establishing permanent teams is the most effective from a performance point of view. Replacements or additions to the team are easily incorporated.
Compare this with the situation in a matrix management system. Here the teams are loosely integrated, they are temporary, and they go through the Forming, Storming, and Norming phases on a regular basis - with the resultant negative impact on efficiency and effectiveness.
A clear indicator of project performance is the amount of matrix management involved, the more the matrix the less effectiveness, at least during the all-important starting phase of the project. Matrix management helps to invoke Briers law, which states: that it's never to soon to start failing. The time lost in perpetually re-creating teams greatly affects the ability of teams to deliver projects on time.