I think that it depends on how you wear your hair. If you blowdry your hair often and use a lot of heat, your ends will get raggedy faster than someone who wears protective styles most of the time which means that you probably should trim more often. On the other hand, if your hair is constantly protected, you are not doing anything to damage the ends and will not need to trim very often. Personally I don't believe in getting scheduled trims and almost had fight my EX-hairdresser about this. If my ends don't look bad then I see no reason to cut/trim them. JMHO