Hiring a Guava libraries developer is beneficial as they can leverage this extensive library to improve the efficiency of your Java-based projects. Guava provides utilities for collections, caching, primitives support, concurrency, common annotations, string processing, and more. A Guava developer can use these utilities to write cleaner and more readable code, making the development process faster and more efficient. Their expertise can help in reducing coding errors, enhancing software quality, and improving overall application performance. Thus, a Guava libraries developer can add significant value to your Java development team.