It depends; if you have characters that need Cor Lapis for their ascension, then you have to farm 168 Cor Lapis for each character to take them to their full ascension, which is level 6. I'd recommend you farm a bit more for any future characters who may use Cor Lapis for their ascension. Whichever material you're farming, it's always better to farm a bit extra to avoid running low on them in future. Genshin Impact introduces new characters and weapons with updates, so always be prepared. If it's not a new material to the game, you'll be on the safer side.