This plastic clip protects the wires that attach to the print head on the Printrbot simple metal. It attaches to the Y-arm, right over the fan and holds the wires away form the other moving parts. It can prevent the wires from:

1) getting pinched between the extruder motor and the Y axis motor.
2) jamming the Y axis causing belt-grinding or misprints.
3) internally breaking from repeated bending near the motor.

Issue 1 and 2 happened to be repeatedly. Issue 3 was a problem my friend had after running a printer for a year. It was a difficult problem to find and fix.