For 4 , and 2 you force the Corp to spend at least , potentially as much or more and ice to defend Archives. Combined with Desperado, you'll earn your spent on Sneakdoor within a turn or 2. Combined with Doppelgänger, you get an additional surprise HQ access that turn. If you are running a typical 3 breaker suite and a Console, Sneakdoor is an absolute must (especially for Gabriel Santiago: Consummate Professional!) Nothing makes the Corp bitter more than having to dedicate time and resources to defending a mostly obselete server.
Combine with Emergency Shutdown, HQ Interface, Nerve Agent and other HQ-hate goodies!