Many times, users print just 1 black mark to save media loss like below.

It is OK, because black mark sensor and CCD camera are always watching wall-side marks.

However, please remember that you always  need to use 2 marks for cutting files, even though you printed only 1 mark on the paper. Otherwise, the cutter will not be able to determine the right registration of cutlines, which is calculated by 2 marks recognition.