Grails is used at LinkedIn for some projects due to its productivity advantages over Java frameworks. While Grails was productive for new development, integrating it into LinkedIn's large existing Java ecosystem required effort. Challenges included integrating Grails with LinkedIn's custom Spring configuration, sessions, authentication and building/testing practices. Solutions like a Grails plugin helped address these challenges. Overall, Grails was found to be more productive than mainstream Java frameworks for some uses at LinkedIn.