As @gilmorkn472 said Gyroscope could be very useful for autonomous programming, but only on the more advanced after you have reached the limit of the accuracy that quad encoders built into V5 motors could give you.
If you have an easy time understand math in 5225A tracking document and QCC2 Gyro code, and you could imagine yourself spending two months in the summer perfecting your autonomous navigation, then Gyro is a good investment.
Accelerometer, on the other hand is less useful. The best usage for it, as far as I know, would be as a tilt sensor and, also, to detect possible collisions with other robots during autonomous.
Over the last few seasons the only time we found a good use for it was during Skyrise. If the lift was extending all the way up and would start to tilt we used accelerometer to detect it and limit drivetrain acceleration in the direction that would make tilting even worse.