The grooves or slots are made to keep the brake pads cool during heavy braking hence minimizing brake fade. This is why you see many high performance cars with them. These brakes are manufactured using very exact standards. These are not something that somebody decided to do at home by drilling or grooving their own brake rotors.
Cross-drilled holes are drilled by CNC machines programmed to drill rotors specifically for the application. The holes are drilled completely through the face of the rotor, enhancing airflow while maintaining structural integrity and perfect balance of the rotor. Cross-drilling allows efficient ventilation keeping the rotors cool.
Slotted lines are designed specifically to help remove water, dirt, and brake dust build-up between the brake pads and rotors. With slots brake pads are deglazed improving contact between the pads and the rotors shortening the braking distance while increasing the effectiveness of brake response
Advantages are that if properly used with the correct brake pads, they will keep your brakes fade free.
Disadvantages are that these holes and grooves can weaken the rotors and cause stress fractures.
Use your own judgement, but only install proper manufactured rotors from reputable companies such as Brembo or Bosch. If these are not available, look at original parts from the manufacturer. Brakes are some of the most important pieces in your car puzzle. If you really want to increase your braking performance, you should get either Semi-Metallic Pads or if possible, you can get Ceramic Pads. The Ceramics offer superior braking performance. In any case if your upgrade your pads to these types, you should also upgrade your rotors as well.