Phew, I just love it when somebody does (mass-)changes without being aware of the implications. Thanks for reverting this, though. At DB we use these data for showing the station maps and it screwed up just about everything. Luckily I am checking most of the changes before putting the changed data live.
IMO: light_rail is nearly always S-Bahn (with some exceptions), while rail is normal rail traffic. Layouting is almost always different (non-dashed line vs. dashed line). If in doubt, ask somebody or consult the OSM guidelines, they are very good. 
FYI: there is some controversy between lightrail and tram depending on how it is operated, but layouting there is at least the same.