The site analysis is also key in understanding the nuts and bolts of your site like soil condition, sun/shade and various other factors. There might be elements in your garden that you might be keeping that would be important to note. The concept drawings are also equally important as they allow you to get a first hand look of what is possible in your garden. This is where the designer will meet with you to go over the concepts and you get to voice your opinion. This video explains that entire process and much more.
You can watch the other design process videos here: http://tinyurl.com/y8ftydfe