Seriously? Maybe people make too big a deal of this. I've seen plenty of quick jobs that turned out just fine for years. Sometimes good enough actually is good enough.
Laura_carter's story about moisture problems shows why rushing fails. I see this in many areas, like when people skip prep work on paint jobs and end up with peeling walls. Taking time upfront saves so much trouble later.
Wait, do people really just throw insulation up without sealing gaps? I saw a friend's place where they did that, and now they have cold spots all over the house. Moisture got trapped in the walls and made a big mess. Taking a few extra days to cut pieces right and use vapor barrier seems worth it to me. How can anyone think a quick job is fine when it causes so many problems?