The braking resistor is a mechanism used to decrease the spin down time of the spindle. It is 300 Watts & 250 Ohms. By default, your spindle is setup to have a 6 second spin down time. The braking resistor allows you to set it lower without error and as low as 3 seconds. 

You will need a V5 VFD for the appropriate plug and an upgrade package from any lower version can be purchased here. This will not work with the buildbotics problem where it spins for ~>20 seconds as described here. 

If you want to try and set it lower you can but if you experience an Err06 the first thing you should try before contacting support is setting it to 0003.0 or higher. The 3 Second time is not promised reduced spindown time as its just as low as we have been able to achieve in testing.

In order to change the settings on your VFD you will need to hit mode, then navigate to P0.0.12 using the up and down arrows and double right arrow to navigate to different points. As stated earlier this comes preset to 006.0 which equates to 6 seconds and with the braking resistor you can set it as low as 003.0 without error, however your results may vary.