Whether it's Ils, The Strangers, Straw Dogs, Funny Games, or even The Purge all home invasion films begin with getting to know the family. Most horror dictates that the audience should learn about its victims and gain a connection prior to their destruction. It is believed that our caring of them and their lives before the disaster will make the impact of their situation even more dire.
This is true, nearly all the greatest horror films follow this formula. No one would feel for Reagon had they not seen her as a normal girl prior to her possession. Even the mindless fodder of Sally's friends provides a perfect build-up to meeting Leatherface. Without knowing the crew of the Nostromo, John Hurt's chest bursting scene would have fell flat. We would not cheer for Laurie Strode, had we not spent the boring day with her. So when Morlet omits this build, how does it affect the overall narrative?
We begin with a man entering a home and deactivating the alarm. He proceeds to wander the house and through his curiosity we learn the home belongs to a couple with a child. The answering machine lets us know the kid is staying with a family member. After the faceless intruder is finished snooping he prepares the house by screwing all the windows shut. He then dresses himself in hazmat gear and dons a frightening mask made of wood.
The variation on the normal horror narrative gets under your skin, because without the couple present, the house he is in - is yours. He is going through your stuff and awaiting your arrival. This is terrifying. When the family does show up, he lets them get comfortable while we are anticipating his next move or who he will 'get' first. As we had feared, the couple themselves were a little annoying, but overall it does not matter since they only get a few minutes worth of dialogue.
When the killer makes his presence known the sequence is intense and the suspense doesn't let up until the end - and speaking of the end: you will get more than you thought you would out of the film.