For example :
You are decoding a block coding such as RS, and 255 symbols are stored temporarily.
After complicated decoding procedure, you will fetch the stored symbols for correcting after some period of clock.
Since the mechanism is ensured, you will only stored the received symbols in the FIFO once the output answer is generated.
Because of that, the FIFO is never full and thus it's unnecessary to check out the status of FIFO.
In the other words, since the designer always knows the status of FIFO, it's redundant to check out the flag again.