The stuff on Yoox is never used, unless it's in their Vintage section. Everything else is just unsold stock from designers and boutiques, designer runway samples, etc. Think of them as a high-end fashion-only version of Overstock.com.
Most of their stuff is only a year old, with the exception of pieces that are special enough for them to think it's worthwhile rotating it through the site again. They're only lagging 2 seasons behind on the majority of their inventory, which is not so bad.
They tend to start the prices pretty near the original full retail price, and a lot of people buy stuff at that price because let's face it, there aren't a lot of places you can buy Balenciaga, or Carol Christian Poell, or Junya Watanabe, etc. If you live in Montana, Maine or Mozambique, Yoox is going to be your only option.
Even living in Paris, you'll find there are going to be pieces that don't get bought by any stores in France, but maybe they were bought for the Italian market or Japan or the USA and later show up on Yoox. So why not pay almost full price, if you really love the item?
If you don't love it, you stick it in your Dreambox and wait for the markdowns. By the end of the season, everything that's left will generally be selling for 70% to 75% off the original Yoox price.