Power factor should be high in order to get smooth operation of the system.Low power factor means losses will be more. it is the ratio of true power to apparent power. it has to be ideally 1. if it is too low then cable over heating & equipment overloading will occur. if it is greater than 1 then load will act as capacitor and starts feeding the source and will cause tripping.(if pf is poor ex: 0.17 to meet actual power load has to draw more current(V constant),result in more losses if pf is good ex: 0.95 to meet actual power load has to draw less current(V constant),result in less losses).
Power factor should be high in order to reduce the line losses,. The low power factor cause reduction in utilization of available MVA capacity,