SketchUp is somewhat an odd out out when it comes to backfaces. Most other 3d modelling apps doesn't even display backfaces - if you look from the backside it'd be transparent. Unless you explicitly told it to display backfaces.
Id' not say it's good modelling technique to keep backface with no material, but it is good practice to keep control over frontface and backface orientation and keep them consistent - making sure the frontfaces are the ones visible.
When you have consistent and regular normals you have a more predictable mesh which makes modelling tools act more reliably. There aren't that many functions in native SU where this matters, but there is some. And plugins and extensions - in particular render engines cares much more about this.
Some doesn't use SU's backface materials, some do. VfSU for instance do that by default. But you will find odd things happen when you try to displace a mesh if you have faces flipped this way and that - as the displacement height is dictated by the face normal.