Do we need projection rule to create object in CS?

Experts,

I understand that if we want to create an object in Metaverse during synch from CS, projection rule is required.

However what is the case during data flow from Metaverse to CS. If i just defined joining rule, will object get created in CS(If object is present in Metaverse) or do I need to create projection rule.

Kindly suggest I don't have hands-on experience on FIM.

Thanks,
Mann