Nowadays, responsiveness is essential to be competitive, particularly in software development. Traditional methods face limitations in meeting this demand for agility, which led to the rise of agile practices. Inspired by their success in small projects, organizations have begun to use agile methods in larger contexts. However, scaling agile practices introduces complexities and requires coordinating teams, managing dependencies, and collaboration. Communities of Practices (CoPs) are argued to address these issues and support organizations in adopting agile methods at scale. Still, empirical insights into the establishment of CoPs in scaled agile settings are limited. This study fills this gap by conducting expert interviews, exploring why organizations applying agile methods at scale adopt CoPs, and examining their characteristics. Our key findings include that, next to benefit from known advantages of CoPs, like knowledge sharing, organizations establish them to foster empowerment, drive their agile transformation, and strengthen alignment. Moreover, CoPs focus not only on agile but also on classical themes such as architecture. Communities are not necessarily established bottom-up but are often initiated by management, e.g., to empower employees. In general, CoPs are accepted by management and play an essential role in decision-making.