For the shooters, guaranteed a rather hazard free opportunity to maim and kill as many disarmed humans as they wished or found the time for.
The FBI apparatchiks define a mass shooting as four or more people killed and/or injured during a single shooting incident, and that definition typically is widely accepted by law enforcement agencies, criminal justice experts and the media. One can see the NYPD providing a demonstration here when they shot nine bystanders while trying to apprehend a shooter. Please note that the geniuses in the thick black and blue line charged the man they were shooting at with the casualties.
Only in Amerika.