We do add a lot of perspective views of details and parts of the building. We just don't want to spend the time to detail everything we need to put on paper in 3D. That's why we also use an application like Vectorworks.
I added another example of how complicated it is to completely depend on 3D work in Sketchup yet. In this example you see a few pages of the work done in 3D with Sketchup.
Please don't click the link of you are on a slow connection, this is a 18 Mb file.
https://www.dropbox.com/s/8cmhutqyfzbxuhz/FILLIEVRHOEVEN-EXAMPLE.pdf
Contractors here in Holland subcontract maybe over 80% of the work. They need contract like drawings with very strict dimensioned layouts. In most cases parts are made directly out of our drawings including windowframes. All windowframes are custom made exactly to our specifications and requirements for warranties. Imagine to have to do all this in 3D. Up to now we find ourselves trying to do the impossible in 3D. We want to work in 3d since we do understand the advantages. We haven't found the app or system yet to get it done the way it is required to do.
Something we don't want to do is highly detailed work in 3D as well and seperatly in 2D. Double work as nobody likes. Another thing is we don't want to get stranded in 3D slowing down our workflow or even worse, not getting it done at all and redoing stuff in 2D later on.
I hope the near future brings a single 3D workflow getting the right kind of abstraction like we have in 2D that is easy to work with and understood at the building site. You simply need to be able to meausure dimensions from paper or on an iPad to be able to improvise on site if needed. With an iPad this could be done in 3D but without it I don't now how you could from a perspective view.
Francois