One of the good things, when we have new clients, is that sometimes they have needs that you never heard before. This does not necessarily mean that they are complex. As a matter of fact, they can be really simple..now the question is..are they doable? :-)
From my experience, this can happen mainly because one of two reasons, they have some very specific need, or because the way the application is built will make you work with features that you haven’t played yet.