A CRC-n method is mainly used to protect the communication against a wrong frame alignment word and also to provide a certain degree of monitoring of the bit error rate when this has low values (around 10-6). This method is not suitable for cases in which the bit error rate is around 10-3 (each block contains at least one errored bit).

Another advantage in using the CRC is that all the bits transmitted are checked, unlike those systems that only check 7 bits (those of the FAS, which are the only ones known in advance) out of every 512 bits (those between one FAS and the next). However, the CRC-4 code is not completely infallible, since there exists a probability of around 1/16 that an error may occur and not be detected, that is, 6.25% the blocks may contain errors that are not detected by the code.