The title pretty much sums it up. I find that using potions or equipping items that enhance Smithing really don't do diddly squat.

I thought that with a 30% smithing enchantment, armor that would normally have a 50 point defense would now be 68. Nope. The armor I crafted with and without that enchantment bonus were exactly the same. So then I thought it would increase my Smithing skill, not the quality of the armor by that same percentage. If it did, it was not evident in the skills menu. Using the enchantment or not, my skill remained the same. The only thing that seemed to have any effect was when I used two enchantment (item + potion) which totaled 50%. At that point, I was able to smith some armor at one level higher than my skill would allow. Big deal, right. All one has to do is smith a bunch of rings and necklaces or leather armor and boom - you can smith at a level higher that you used to.

So the real question on my mind is this...

Once you can smith at legendary quality, do smithing enchantments do anything at all to improve quality?

If anyone knows different, please share as the entire concept of enchanting smithing looks to me like an exorcise in futility.

Oh yes, smithing potions and enchantments are the key to becoming a god among mortals in Skyrim. Even 30% should have a noticeable effect on the weapon you upgrade, just make sure you have the perk for the relevant material first. However, since all the bonuses are multiplicative, you'll need to get your base skill higher first to start noticing the effects.

Full details on how to abuse crafting in general: http://www.gamesas.com/topic/1342463-complete-character-design-freedom-damage-resist-caps-and-ridiculous-damage-thread-10/

If you want upgraded weapons its essential, for armour maybe less so because of the overall cap but i always think smithing is one of the more useful attributes but its a personal thing as it suits my play style.