Yes, I would use them as "treats" too. I rarely use them, I do have a can of FD bloodworms which the hatchetfish love, but must confess that I rarely feed this, can't remember when I last did.
It was on this forum that I learned about soaking the FD first; apparently the food expands inside the fish otherwise, and this is not so good. I won't say this killed the angelfish, but...?
There is nothing wrong with a regular diet of good quality flake/pellet foods (and sinking foods for substrate fish). A variety of types from good manufacturers (Omega One, Hikari, New Nutrition [if this is the correct name, another member mentioned it]) will provide the nutritional needs. Jack Wattley even writes that for discus this is all you need.