Feeding at least the recommended minimum makes sense for feeds that are primarily for nutrition. I know some horses who get 1/2 lb of grain a day, when the recommendation is for 3-5 lbs. That 1/2 lb is coming nowhere close to providing the nutrition lacking in the hay, so yeah, it's pretty much useless.
Flax is a little bit different- you don't feed it for the vitamin or mineral content, but for the fat. If your goal is just to give a little shine to the coat (as opposed to weight gain/maintenance), then 4 oz is perfectly fine. I used to feed 2 oz once daily to my horse and he had a shiny, soft coat. I ended up increasing his in the winter to 4 oz daily for the omega-3's (no pasture) and increased a little bit more recently because he dropped a little weight this spring.