Extant research has uniformly demonstrated that forming and maintaining workplace friendships benefits employees and organizations. Unfortunately, little is known about its potential downsides, especially the negative spillover effects of such dyadic relationships on organizations. Our purpose is to reveal that workplace friendship is a mixed blessing by investigating why, how and when workplace friendships are likely to simultaneously promote discretionary behavior (organizational citizenship behavior) and non-discretionary behavior (compulsory citizenship behavior). We propose that the double-edged effect of workplace friendship hinges on individual relationship motivation. On the one hand, when employees have autonomous relationship motivation, workplace friendship is positively related to employees’ perceived insider status, enhancing organizational citizenship behavior. On the other hand, when employees have controlled relationship motivation, workplace friendship is positively related to employees’ felt obligation, which triggers compulsory citizenship behavior. The results from the three-wave survey support our hypotheses. In conclusion, our findings reveal the pros and cons of workplace friendship and the importance of recognizing relationship motivation in maintaining the workplace friendship process.