[yash101]

PID is quite required, to my opinion. Last year (2013), our robot did well, but the shooter wasn't consistent because we didn't have a way to measure the shooter speed. We would just place the shooters at 100% power and shoot from the same place. Programming a consistent robot closed loop can be hard because you need to calculate the motor speed using the hundreds of variables, mostly:
-battery voltage
-motor life
-controller life
-load on motors
-bearing stress
-multitudes of other variables
Yes, you could use vision so that the robot can determine whether the disk went into the goal. However, that would be hard because there is a small slot of time where the disk would show the greatest proof of position and landing. Encoders can be a life-changer when you want to want to have a very accurate robot while remaining simple.