That is incorrect: off-target activity is virtually non-existent in CRISPR-CAS9 mediated transformation. Targeting oligonucleotides can be deliberately designed to be less specific, thereby targeting a family of sequences, which is very desirable for e.g. knocking down a gene family. However, specificity is trivial to achieve when desired.
Precision has two components: specificity and sensitivity. While recent versions of CRISPR make it possible to avoid off-target sequences, its impossible to guarantee cutting. Also, while you can make a cut, engineering a specific substitution is still largely a crap shoot. Not suitable for gene therapy.
