Items could be dropped with enchantments. Depending on the enchantment and the quantity of items you got with the same enchantment you could end up with great benefits.
All enchantments are divided into tiers, the better the tier the better the effect.
The tiers are from worst to best: Normal < Rare < Unique < Legendary < Mythical.
You could mix different tiers but not the same tier. That means if you have a full set of Mythical you could not have another full set of Mythical, only 1 Mythical effect going to be taken into account.
Enchantments could be transfered with the Enchant Transfer NPC with some rules.
First of all the item lvl you are going to take the enchantment must be equal or greater than the item that you are going to receive the transfer. That means if you have a lvl 90 item you could transfer an enchantment to a lvl 80 item but never to a lvl 95 item.
Also the transfer could fail, if the item is the same(it means if both are training stones) you have a chance of 90% of success. If it’s another kind of item the chances are 36% only.
Here is a detailed list of all enchantments, with their effects and % of benefit you get when having certain parts of the set.