Why is it significant that all biological systems use l-amino acids and d-sugars?

L-amino acids and D-sugars are part of every protein.
All proteins are made up of them.
The fact that all biological systems use L-amino acids and D-sugars is linked with the idea that certain groups of organisms come from a common ancestor because. The reason is that if the common ancestors used L-amino acids and D-sugars, than its offsprings use them as well.