This lets you use Moonstone and Quicksilver ores to put together Elven Armor. Elven Armor is noteworthy for being particularly light (even for Light Armor), a bit overly shiny, and being the only non-steel armor that forces you to bring multiple types of ingot to the forge. For the most part, Elven Armor sells well in terms of raw price, and the existence of Ornate Elven Armor (for those who manage to scrape together enough ore) gives you a step even further to go before moving on to later armors.
This stands out as being one of the three Smithing perks that lets you make both Light and Heavy armor, and goes even further by matchign Dragon Armor as one of the only two perks that lets you make a full set of either. Advanced Armor enables you to craft both Scale Armor (Light) and Steel Plate Armor (Heavy)- the latter of which is favorably comparable to Orcish Armor from the other side of the Smithing ‘tree’. If you’ve been operating with Light armor and your follower uses Heavy armor, then this perk will give you an opportunity to ensure they are well-clad for the middle and later parts of the game, something that the Heavy armor related perks won’t let you do for a Light armor follower in the opposite situation. Unfortunately, you’re also trading in the chance to make the powerful Orcish weapons to get that opportunity, so you may find that it’s not enough and you want the heftier side of the Smithing perk tree as well.
This perk relates to the curious glass armor and weapons, a set of items you wouldn’t expect to be of much use to anyone if you’re at all familiar with how glass acts when it hits anything harder than a wet towel (hint: it doesn’t stay in one piece). Despite that, glass armor and weapons are a very useful, if fanciful and almost a little silly, step on the weapon scale as well as the light armor scale. The weapons roughly compare to Ebony weapons, and while they tend to be a bit weaker, they also tend to be noticeably lighter and thus easier on your carrying capacity. Unlike on the Heavy armor side of the Smithing tree, there is no armor spot between this and Dragon Armor- so once you start finding your Glass Armor and glass weapons a bit too frail, it might not hurt to take a few trips into all the mines you’ve found so far and dig up a few hundred units of ore to push your way up to 100 for Dragon Armor.