Why do I need two TB gaskets? Are they installed together as one?

About taking off the manifold... The TSB doesn't say anything about dropping fuel pressure or dealing with fuel rails. Yet I saw some posts here recommending to even buy injector o-rings in advance. So, what's the real deal here? Do just like the TSB says (detach TB, then all cables and hoses from the manifold, unscrew and clean manifold and put everything back together), or are there catches and gotchas like fuel pressure release?