As projects involve people with many different personalities (trying to) work together as a team, it it worth the time and effort to have the team participate in a Myers-Briggs personality inventory? Does the answer depend on the size of the team? The type of the project? Should the project manager make decisions about task assignment and communication styles best on the results?
As a project management tool, perhaps not. But I think that it can be a good team-building exercise.
A few years ago, the team that I'm part of all did MBTI, not to pigeonhole us or change task assignments, but rather to try to give everyone a little extra perspective.
It reminded us that we're all different, with different strengths and weaknesses, and that sometimes extra care/effort is needed when communicating with people that don't think in the same way.
I believe such evaluations have little value in terms of working with the team. I assume you already have your team so you don't want to use the method to select people. If I'm wrong here you can also be interested in this question.
Anyway when we're talking about everyday work with people I strongly believe you will learn much more from your interactions with them than from some sort of artificial evaluation. Everyday communication is what will give you the best clues about what kind of communication style you should choose in each case.
If you think about task assignment you're likely to base on competence in the first place and not on the way someone perceives the world (or similar criteria).
In short: I wouldn't invest the time to do such evaluation. However, models such as Myers-Briggs are usually worth knowing so you have some background you can refer to when processing observations and experiences from everyday work with people. From this perspective they can give you better understanding and help you to make better decisions.
I am with Pawel on this. I would not waste precious project resources on doing MBTI or DISC or anything else. The only deviation from that might be if the project was a long term gig and I was having difficulty getting the team to gel, i.e., intervention based on an issue where other interventions failed.
It is interesting, though, and can be helpful when trying to figure out how to deal with someone. In an ongoing operations, I'd likely do something like this. On a project, no.
If your project is long and your team is expected to stay with the project, you may want to invest sometime in doing some testing like this. Often teams will invest in communication style assessment and analysis. Communication preferences are different from myers briggs. They allow you to see how your team members fall into communication quadrants and then support the team in understanding how to deal with each other's styles. One I used with my team was True Colors.
According to my readings, MBTI has effect on team formation. It tells us communication styles of the persons and being aware of it helps conducting effective meetings. It also makes some people more suitable to certain roles more than others and it helps you directing people to career paths they are best at. This all sums up in motivation and making people more effective. But I have to say it's very difficult to make decisions based on MBTI. For example if you organized your team according to MBTI and one of the members had to leave, it's difficult to get or hire someone with similar technical skills let alone his/her MBTI.
IMO, if your organization's structure is functional, it's most difficult to apply MBTI. If it's team based or project based and projects are long enough, it would be easier to apply MBTI. Also it's easier with larger teams than with small teams. It's also easier if the organization does not mix roles so if the developer is responsible for Analysis, Design, Coding and Testing, it will become useless.
So where I used to work, it's been usually a luxury I could not afford.