Why Sketchup,,, Very good question
For me Who is not a pro designer this was my feeling
Sketch up free version is a Perfect starting block for floor plans and so easy to learn in five minuets turn a sketch on the back of a ciggy packet to a working drawing and it doesn't cost you a penny to produce but your time, as you click you have walls with the advance users Model database you and furnish that model produce a working concept that just landed you a paid contract. as your skills grow (others here very advanced) With no need to understand meshes and all the information you need to use max 3d (Auto Cad products)and other alike and not forgetting the cost to pay to train and learn them packages on top of the price of software mounts to £1000s,
After 6 months of learning sketch up from Free Forums and U-tube, all it cost me was my free time I purchased pro with the Lay out export option saves so much time with sending out plans to clients, thanks to all the Skilled people here the tips plug'ins and much more and (Kerkythea Team) I have learned 1000s of pounds worth of knowledge.
So end of the day i Love the speed the quick response i get from sketchup, the support and advice from all the users, the last time i used a 3d package was Light wave with Amiga 040/video toaster for fun with friends as they gave it away free on Amiga format.
So to date thank you to the team here for all the tips and advice that no other 3d package has that support And that's Why Sketch up Is the one