If the CRISPR/Cas9 system had not been adapted to eukaryotic cells, it would never have generated the kind of buzz it did. We are excited by this novel protein system because we can use it for precise, targeted genetic engineering in humans, animals and plants.
A lot of ongoing research is focusing on treatment of genetic diseases in plants and animals. However, if this system is ever to be FDA-approved for disease treatment, any and all off-target effects need to be mitigated. As Wu et al (Quant Biol. 2014 Jun;2(2):59-70) and a plethora of other similar papers have shown, we are far away from achieving this goal.
This is why I think impact of off-target effects on CRISPR as a tool is enormous.