becoming is friendly is good . it gives us happiness and an exciting atmosphere people who lives in this kind so atmosphere not only they become happy but they get good result also.
as per my short experience with some of employees whenever i smile and laugh with them then they think that our boss is genuine and generous to the employees. but it doesn't mean that you create friendship with your employees
you may lose your target if you do so. whenever they become friendly it means they are to know you weakness