The first time a buyer of one of our new homes hired a home inspector before closing, I was a bit perplexed. I mean, this was brand new home, and I didn't think there were any issues that justified a home inspection. But now, after experiencing a handful of them on new homes, I have concluded that it's a good idea.
In my experience as a builder, I'd say that about 90% of the issues found by the home inspector were things that were already on my list to take care of, and the rest were small, seemingly insignificant things like a speck of paint where it shouldn't be, or a spattering of mud that somehow made it onto an interior wall. So, overall, the inspection helped me to appreciate the level of quality we were building, but also to focus on the really small, but important details that can be overlooked.
But the really important stuff can get missed, too. I know a family that lived in another builder's new home for half a year before finding out there was no insulation in the attic! The local building department in this particular area had signed off on everything, and the new owners were clueless until an insurance claims adjuster had to inspect the attic and made the discovery.
The lesson here, is that you never know what you will find. Builders and even building authorities can miss small things, and sometimes they can miss big things. I believe its worth the time and expense to hire a home inspector, even on a new home. If nothing else, it will give you the piece of mind that your new home is as perfect as it can be.