Inventables needs to change what they call the switches that ship with a full machine. They are not limit switches as they are configured on a standard machine, They are homing switches and referring to them as limit switches is confusing people that are new to CNC.
As has been said before there is to much electric noise generated by the brushed DC motor that they call a spindle to be able to configure a standard machine for limit switches. You would also need 5 switches 1 at each end of the X and Y travel limits and 1 at the top of the Z travel. Three of those switches can also be configured as homing switches.
You would also need to do something about the noise and use shielded wiring going to the switches.
When done correctly homing and limit switches make a CNC machine safer and easier to run multiple part runs.
FYI limit switches on a lot of CNC machines are configured NC and the 2 X axis switches are in series going to a single input pin as are the 2 Y axis switches in series going to there own input pin. Z axis switch goes to a third input pin.
In configuration pin 1 is Z home and Z+ limit, Pin 2 is X home, X+ limit and X- limit and pin 3 is Y home, Y+ limit and Y- limit. Your pin numbers may be different than the example given.
As also been talked about when testing for proper operation move as far away from the switch being tested and trigger it with a chop stick as the machine moves towards the switch. Set your feed rate low so you have time to react if the switch does not give the desired results. Have your other hand on the emergency stop button just in case.
Hope this helps.
Dave