This allows you to choose between low requirement gear to put more attributes into en or vit, or higher requirement gear because you have either a dex/str build or you want more defense. Item bases make the the attributes (str/dex/vit/en) matter more when allocating them. I think its important to cover Item Bases (tiered items) and mystic obs (attributes that you can purchase from a vendor) There are things about median xl that a lot of people don't/won't like about this game, but I just want to focus on itemization as I think they have done Crafting, Runewords, Uniques, Sets, better than any RPG I've seen.