At what stage of Interior/Architecture designing do you use SketchUp?

For a typical design project, do you use Sketchup from day one of your client engagement? Or, do you conceptualize your design using 2D and/or hand-sketches and come to SketchUp for detailed 3D designs/rendering alone?

Please share your experiences.

I have a background in Fine Art and illustration, but I never pick up a pencil any more.

My design process is explained in this post - Concept design

To summarize, I do a lot of research and visualization before I start to model with a clear idea of direction.