The majority of construction tasks (foundation, framing, plumbing, electrical, etc.) are usually subcontracted out to the lowest bidder, with speed, not quality being an important consideration for the builder. With many separate activities going on at the same time, it’s nearly impossible for the contractor/builder to personally monitor all phases of the home construction.
Don’t assume your builder — or the contractors — did everything right just because the home passed code. An inspector is your last line of defense against major defects that could quite literally sink your financial future.