While sigil stones allow you to add great effects to weapons and armor that you can't get by yourself, I can tell you personally that I closed every gate in the game and didn't bother to use one of the stones. There were a couple I liked the armor enchants on, but I had all daedric armor with +10 to strength or other attributes. And if you want a good enchanted weapon, just do some of the daedra quests or guild quests.