The paper takes CRISPR/Cas9 and turns it into a targeting system for an set of enzymes that allow modification of a single DNA basepair at a specific locus in the DNA without introducing a double strand break.

The reason this is important is because a double strand break (the result of standard CRISPR) is a devastating event, introducing a risk of uncontrolled mutation. However, if you're able to modify a single basepair in the DNA in a targeted fashion, you eliminate that risk, making it much more practical to use this technology in the clinic.

There are still absolutely massive obstacles to using CRISPR in a clinical setting, but this is a very important step forward. It still remains to be seen how you get the CRISPR/CAS system into a cell (and other ancillary accessories specified in this work) reliably in a clinical context. Still early days, but a very important step.

Full disclosure: David Liu (the PI on this work) may be seen as a competitor to the lab where I did my graduate work.