I am sure someone will tell you to download the DCS companion book from the MTH website, and it is definitely worth doing.
The problem with DCS and Buss wiring is that with DCS, you can't have more than one signal connection in a given track circuit (for visualization reasons, assume the track is set up in blocks). If you have multiple DCS signals coming into a particular block, it causes problems from what I have read). DCS uses the middle rail (the power rail), and the first thought most people have would be to use the buss for the power rail to deliver the dcs signal. The problem is that each feeder off the buss would be delivering, not just power, but a DCS signal, and that would cause the problem.
When I wire for DCS the power and the DCS will be seperate, each block will only have one dcs connection and multiple power feeds as a result. The same is true if you don't use block wiring, you could have only 1 DCS connection on the whole layout, which is why I have been told even with command control it can make sense to have isolated track blocks/sections, even if not using block control.
