Surgery is usually advocated to lower the eye pressure if drops have been insufficient or if you are allergic to topical medications.  The advantages of surgery are:-

1  Lower intraocular pressure

2  Reduced requirement for drops

3  Better diurnal control of intraocular pressure. This means that the pressure does not fluctuate much during the day. In patients taking drops alone, the pressure variations can be quite marked in some patients (up to 8 mmHg)