I personally have never used it for "bulking" purposes alone. I use it everyday because of it's a good source of essential omega-3 fatty acids. Studies of flaxseed oils efficacy are inconclusive, but believed to provide benefits for arthritis and lupus patients by reducing inflammation.
I remember a client of my wife said she always had trouble going to the bathroom regularly. So I recommended Flaxseed wich acts as a bulk-forming laxative for treating constipation or infrequent bowel movements. The seeds, flax meal, or powders absorb water in the stomach and intestine, increasing the bulk and movement of the stool. Some time later I saw her and was proud to say she was going more frequently to the bathroom.
It's great for your hair, skin, nails, digestive system. SO to only use it when you are in a "bulking" cycle would be short changing this very important everyday needed use product.