Agree with honkit - it really depends on how many fishes you have and how much you are feeding them. Also, it depends on your husbandry methods... If you are diligent and keep to tab your water changes at once per week, you can do away with very little GFO (assuming your stock level is within limit).. a couple of factors involved.. not really so straightforward...
For myself, I am running minimal GFO, but I do put liverocks into my sump for filtration and maintain a small list of nano gobies and 3 chromis in my two feet tank...