What are the applications of knockout cell lines

Question

The CRISPR/Cas9 system is an adaptive immunity system in bacteria against bacteriophage invading. It has been developed as the most popular method for genome editing in recent years. The engineered CRISPR/Cas9 technology consists of a single guide RNA (sgRNA) and a human codon-optimized Cas9 nuclease. The sgRNA recognizes the genomic target via standard Watson–crick base pairing and acts as a scaffold for binding of the endonuclease Cas9.