It is true that spacers are mainly used for esthetics.
In my case, I'm using them to clear the brake calipers (front) on my LR4 to be able to fit 18" LR3 rims.
The actual real use for a spacer is to widen the track in order to have a more "planted" vehicle when taking corners at high speed. Their main use is track, a lot of people will use them in rally racing as well as off-road racing as the wider stance track keeps the vehicle more stable.
If you already have a low offset, using spacers might push the wheels out the arch (which could be illegal depending where you live).
As for me, I'm happy to be able to have 18" tires and I can not lie the truck looks really badass like this
