Some people think rail joiners should not be soldered, in order to allow expansion/contraction of the rail with changes in temperature, but I have never had a problem with distortion of the track because of soldered rail joiners on my layout (2-rail code 148 track).
I don't understand the point of soldering and filing a rail joint without using a rail joiner: if you are going to solder the abutting rails anyway, why not add the mechanical advantage of a rail joiner? The rail joiner becomes almost invisible after it's painted and it serves to keep the rail ends securely aligned.
I think it is important, whatever system you use, to solder an electrical feeder wire to every section of track, no mater how short. I have wired my layout this way, and the current supply is therefore completely dependable.
