CRISPR/Cas9 allows you to add a gene to an organism’s genome…

CRISPR/Cаs9 аllоws yоu tо аdd a gene to an organism's genome or create a loss-of-function mutation. Besides the end effect (adding a new gene vs deletion/loss-of-function of a gene) what is the primary difference between how CRISPR leads to addition vs loss-of-function of genes?