This is not a required item, You don't need it unless you have one of the problems listed.
WHAT ARE THE SIGNS YOU MAY NEED A RC FILTER ON THE TRACK BUS?
Do you experience the following?
1) loss of train control but not running away. To learn more go here: Loco Runaways?
2) Runaway engines (Take off) : To learn more go here: Loco Runaways?
3) Loss of decoder programming. To learn more go here: Decoders lose programming?
4) Decoders blowing up. To learn more go here: Decoders blowing up?
5) Any combination of above.
Then you should consider installing RC filters on the track.
WHERE DO I INSTALL THE RC FILTERS?
Put the very first one on a given track bus at the FAR end of long track bus run.
Repeat for every track bus you have. Why at the FAR end? The booster already has some RC filtering capability built in which covers the starting point of the track bus. The RC filter you install will provide the same capability at the opposite FAR end. Together they work on filtering the middle of the track bus. A divide and conquer approach to the problem that has it roots in engineering principles.
A snubber can easily be made from common parts available from Radio Shack or other electronic parts stores. You can also purchase ready made NCE snubbers go here to buy now
5240305 Snubber 2 pack of DCC Track Bus Noise Suppressor $12.95