"qu l'on peut acheter..."

Question

In the sentence "Au final, ce que je préfère avec la Saint-Valentin, c'est trouver les chocolats à prix réduit que l'on peut acheter en général le 15 février dans les magasins !" what is the purpose of the "l'" before on? Merci !

Maarten Kamp · Accepted Answer

Bert, 
A common question ! 
This a ‘ euphonic ‘ feature. It is formal, and optional. It has no meaning in its own right, and doesn’t change the meaning or emphasis of anything either. 
 See link for more discussion on when and why it may be used. Note that it is not regularly used in everyday speech, but is still heard sometimes and is encountered relatively frequently in formal writing. 
https://www.lawlessfrench.com/grammar/on-vs-lon/