the grounding installed by nissan isnt the best, doesnt use the best connectors or wire. this can lead to electrical noise through the wires which is then picked up by the ECU's and can distort some signals and slow them down or give them false readings. by improving the grounding you give the ECU's cleaner signals to work with and thus improve their reponse time and accuracy. generally people report that installing this can smooth the idle of the vehicle. it may also have other positive effects which are unnoticable to the user. I cant see there being any drawbacks to this mod whatsoever. IMO i would say it is a practical mod and looks good too.