The braking resistor is mostly for when a motor is connected to a load, for example imagine a motor connected to a 10ton flywheel and somebody hits the emergency stop button. There's a lot of energy to get rid of in a short space of time and it's the resistor that dissipates this energy, obviously a spindle in our application does not have a load connected.
Also re. ramp times, in the ABB I use on my pin router I have the normal ramp time set to something over 5 seconds (can't quite remember) but I can set another ramp for emergency stop situations and this is set lower and for this I use a braking resistor (because I already had one) which allows it to stop very quickly but in reality it's not doing a lot. Also the resistor is there to prevent damage to the drive, depending on how much protection is built into it the DC link voltage can rise and cause damage.