SketchUp or hand sketching

[Jacob]

Functional sketching or drawing-board work doesn't have to be "good" it just has to useful and/or accurate, as necessary.
Pencil/paper are essential IMHO.
Sketchup is just an accessory - with a very steep learning curve which may not be worth the end result! Can't be bothered with it myself.

 

[Brentingby]

Yes, SketchUp has a steep learning curve for some people. Not everyone has trouble learning how to use it, though. For those people who do, paper and pencil is a good alternative. Even for those who find SketchUp a useful tool, paper and pencil is still essential.