Tony,
FTP has the advantage over Content Manager in that, it is possible to download a route without dependencies and save it anywhere convenient. Then, it can be imported into content manager and, as ingha has stated, it can be checked to see if it is of real interest. Secondly, of more importance, its dependencies can then be checked to see if there are an excessive number of "Unknown Assets", including those hidden in DLCs, in which case the route can be simply deleted again as an unwarranted waste of time and effort searching for them all and/or downloading thousands of unwanted items. A third advantage of FTP is that it may be possible to see what version of Trainz it will work with and what is missing from each version.
Until Content Manager has these capabilities, FTP will always be preferential over Content Manager.
Mike