OPEDs or not OPEDs - this is the question

another question that bothers me is that many fansub groups releasing not only subtitles but full series prefer to cut episodes from OPEDs and seed OPEDs separately. this would be OK since this way the overall size becomes smaller and thus is easier both to seed and store... if not for my perfectionism >____< I want OPEDs to be as they are because they contain different list of seiyuus depending on the episode

why? 'just in case'