if u r confident of your light intensity and water flow, its ok not to add coral food.
but people alwaes add and thus shops alwaes haf stocks for coral food cos it helps to boost the growth and appearance of the coral.
besides, if u haf sponges, copepods and tube worms, all rely on coral food to grow nicely so no harm adding.
just don't add to much or u might get too much algae growing.
i use aquapharm coral food....no problems with that