I have a query about L3g4200d gyro:
With what Bandwidth and Cut-Off (Defined In CTRL_REG1) related to ???
I am not sure if I understand what you are asking. The Bandwidth and Cut-Off in CTRL_REG1 are bits that can be set for the Output Data Rate (ODR). Table 22 in the L3G4200D datasheet shows the frequency resulting from the combination of those bits. This video on how to read gyro datasheets might also be helpful.
I mean to say that resulting frequency is for what ??
It is the frequency of the movement detected by the sensor. Setting a low pass filter appropriately might help you to filter out high-frequency vibrations that occur when you are trying to detect low-frequency movement.