If you want just one detail, the only viewport choice given for the layout is Top. What if you want a single-detail layout page based on Front or Right? Unless I am missing something here, currently the only way to do this is to first create the layout with one detail accepting the default Top view, then double click to activate the detail and change the view to the one you want.
Strictly, you do have the alternative of creating the the layout with Initial Detail Count = None and then using the _Detail command to add a detail area using the view of your choice. However you have to specify the area this occupies on the page, making it clunkier than the modifying approach.
I seldom use Layouts, so this is just a papercut for me, but I can see that someone who uses single view layouts a lot would like some TLC here.