The Archive will be the location for researching new Veins of Evil unlocks. As your researchers focus their efforts over time, their discoveries will aid you in choosing just how you want to play the game. At the same time, the Archives is also a way for researcher types to train and even some units are entertained by simply sitting down and reading a book.
Within the musty tomes preserved within this room's walls lies the knowledge of centuries - passed on from one unholy member of the occult to the next. The Archive will entice Cultists to your cause who will pore over the volumes, increasing the rate at which you progress through the Veins of Evil.
Apart from its role in the creation of Sins, the archive also is used to store and identify artifacts - should your workers find one, they will drag it atop one of the work stations, and your researchers will identify its function while continuing to research sins for you at the same time.
One last thing - there's a reason why only specifically trained researchers are allowed to work in the archive. More than one Gnarling has had his face eaten by a particularly irritated magic book, and we still couldn't coerce the Tome of Shadows to release the soul of that one luckless crackpot.
Upgrading your Archive will allow your Cultists to gain experience whilst researching.