SketchUp was apparently designed for users who are not experienced in 3D; it has a familiar a 'Photoshop-tools-palette' type interface (not millions of things on the screen like pro 3D apps) and tools that seem to mimic the way you think about 3D - the push/pull tool that lets you extrude objects is so logical and easy to use.
There is a massive online community and hundreds of tutorial videos and tons of content available to help you make your models.
Overall though, it's the simple approach to creating models that I love. Even though the concept of creating models is intrinsically complex, the tools and interface in SketchUp give inexperienced users a great way to get into 3D.
We need to create 3D models in-house for software testing; using external 3D skills resources would be too expensive. SketchUp gives us the ability to quickly create something perfectly suitable without much effort, and zero cost.