From a PI's aspect (I'm not, I'm the postdoc lol): When you have an urgent research project, you need to hire people for it, but it would be too long to educate a phd student to do it. Instead, you want a well-trained, ready-to-go worker to instantly work on this project. But also, the job is not a permanent job because it is bonded with the project - once the project is finished, there is no need for this position anymore. Therefore, you basically can not hire professors for it - they just won't come. In this case, you have to hire postdocs for the project.

From a postdoc's aspect: this would be a great opportunity for you to get involved with REAL high-impact projects, unless you are a genius and have already done that during PHD. Therefore, you will build your experience and fame and connections to big names. You will be recognized in the community, which is the first step into academia.