I know me neither but I just saw my henniocus butterfly pick on my rabbitfish like it was cleaning him and I'm sure it wasn't hurting him because he was just waiting there until the butterfly was done
certain ones in he wild SOMETIMES have to adapt to eat parasites when there is no other food at the time of year or change do to temp ect... in a home aquarium it will generally not do to food being present
but this is what i have learned from research
for example most copperband butterflys eat aptasia but after they getused to being fed you may find them to not bother picking at them anymore same goes for sixline wrasses